Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $165.86   13.136%   $187.6474   $187.65   $187.65   $187.60  
  Purchase #2 $104.54   7.573%   $112.4568   $112.46   $112.45   $112.50  
  Purchase #3 $148.28   3.647%   $153.6878   $153.69   $153.70   $153.70  
  Purchase #4 $159.96   12.264%   $179.5775   $179.58   $179.60   $179.60  
  Purchase #5 $239.52   10.514%   $264.7031   $264.70   $264.70   $264.70  
  Purchase #6 $143.74   5.233%   $151.2619   $151.26   $151.25   $151.30  
  Purchase #7 $183.79   12.807%   $207.328   $207.33   $207.35   $207.30  
  7 purchase totals = $1,145.69       $1,256.6625   $1,256.67   $1,256.70   $1,256.70