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 $33.74   9.646%   $36.9946   $36.99   $37.00   $37.00  
  Purchase #2 $173.79   13.544%   $197.3281   $197.33   $197.35   $197.30  
  Purchase #3 $59.77   10.356%   $65.9598   $65.96   $65.95   $66.00  
  Purchase #4 $152.50   12.567%   $171.6647   $171.66   $171.65   $171.70  
  Purchase #5 $250.76   8.365%   $271.7361   $271.74   $271.75   $271.70  
  Purchase #6 $53.64   5.685%   $56.6894   $56.69   $56.70   $56.70  
  Purchase #7 $187.79   11.849%   $210.0412   $210.04   $210.05   $210.00  
  7 purchase totals = $911.99       $1,010.4139   $1,010.41   $1,010.45   $1,010.40