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 $69.86   8.349%   $75.6926   $75.69   $75.70   $75.70  
  Purchase #2 $146.33   11.541%   $163.2179   $163.22   $163.20   $163.20  
  Purchase #3 $194.75   8.690%   $211.6738   $211.67   $211.65   $211.70  
  Purchase #4 $239.85   3.411%   $248.0313   $248.03   $248.05   $248.00  
  Purchase #5 $184.66   11.352%   $205.6226   $205.62   $205.60   $205.60  
  Purchase #6 $202.51   12.443%   $227.7083   $227.71   $227.70   $227.70  
  Purchase #7 $27.83   7.613%   $29.9487   $29.95   $29.95   $29.90  
  7 purchase totals = $1,065.79       $1,161.8952   $1,161.89   $1,161.85   $1,161.80