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 $88.32   6.144%   $93.7464   $93.75   $93.75   $93.70  
  Purchase #2 $197.37   12.182%   $221.4136   $221.41   $221.40   $221.40  
  Purchase #3 $53.83   13.760%   $61.237   $61.24   $61.25   $61.20  
  Purchase #4 $194.39   5.648%   $205.3691   $205.37   $205.35   $205.40  
  Purchase #5 $203.58   3.623%   $210.9557   $210.96   $210.95   $211.00  
  Purchase #6 $22.32   11.415%   $24.8678   $24.87   $24.85   $24.90  
  Purchase #7 $188.79   9.174%   $206.1096   $206.11   $206.10   $206.10  
  7 purchase totals = $948.60       $1,023.6992   $1,023.71   $1,023.65   $1,023.70