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 $201.48   12.117%   $225.8933   $225.89   $225.90   $225.90  
  Purchase #2 $141.26   8.468%   $153.2219   $153.22   $153.20   $153.20  
  Purchase #3 $22.87   5.715%   $24.177   $24.18   $24.20   $24.20  
  Purchase #4 $74.35   8.341%   $80.5515   $80.55   $80.55   $80.60  
  Purchase #5 $248.97   5.466%   $262.5787   $262.58   $262.60   $262.60  
  Purchase #6 $87.25   7.219%   $93.5486   $93.55   $93.55   $93.50  
  Purchase #7 $138.75   3.263%   $143.2774   $143.28   $143.30   $143.30  
  7 purchase totals = $914.93       $983.2484   $983.25   $983.30   $983.30