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 $85.69   7.673%   $92.265   $92.27   $92.25   $92.30  
  Purchase #2 $166.99   3.820%   $173.369   $173.37   $173.35   $173.40  
  Purchase #3 $203.44   10.817%   $225.4461   $225.45   $225.45   $225.40  
  Purchase #4 $125.47   10.448%   $138.5791   $138.58   $138.60   $138.60  
  Purchase #5 $213.49   12.535%   $240.251   $240.25   $240.25   $240.30  
  Purchase #6 $245.46   5.467%   $258.8793   $258.88   $258.90   $258.90  
  Purchase #7 $89.57   11.434%   $99.8114   $99.81   $99.80   $99.80  
  7 purchase totals = $1,130.11       $1,228.6009   $1,228.61   $1,228.60   $1,228.70