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 $95.51   7.801%   $102.9607   $102.96   $102.95   $103.00  
  Purchase #2 $218.86   6.751%   $233.6352   $233.64   $233.65   $233.60  
  Purchase #3 $229.72   6.747%   $245.2192   $245.22   $245.20   $245.20  
  Purchase #4 $6.29   7.445%   $6.7583   $6.76   $6.75   $6.80  
  Purchase #5 $229.60   6.117%   $243.6446   $243.64   $243.65   $243.60  
  Purchase #6 $34.47   5.282%   $36.2907   $36.29   $36.30   $36.30  
  Purchase #7 $93.82   10.768%   $103.9225   $103.92   $103.90   $103.90  
  7 purchase totals = $908.27       $972.4312   $972.43   $972.40   $972.40