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 $93.85   8.335%   $101.6724   $101.67   $101.65   $101.70  
  Purchase #2 $238.74   8.390%   $258.7703   $258.77   $258.75   $258.80  
  Purchase #3 $223.89   8.797%   $243.5856   $243.59   $243.60   $243.60  
  Purchase #4 $205.38   12.654%   $231.3688   $231.37   $231.35   $231.40  
  Purchase #5 $135.25   4.550%   $141.4039   $141.40   $141.40   $141.40  
  Purchase #6 $111.65   4.812%   $117.0226   $117.02   $117.00   $117.00  
  Purchase #7 $247.32   4.676%   $258.8847   $258.88   $258.90   $258.90  
  7 purchase totals = $1,256.08       $1,352.7083   $1,352.70   $1,352.65   $1,352.80