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 $56.25   12.187%   $63.1052   $63.11   $63.10   $63.10  
  Purchase #2 $98.79   9.457%   $108.1326   $108.13   $108.15   $108.10  
  Purchase #3 $21.74   4.396%   $22.6957   $22.70   $22.70   $22.70  
  Purchase #4 $215.85   4.562%   $225.6971   $225.70   $225.70   $225.70  
  Purchase #5 $244.68   12.124%   $274.345   $274.35   $274.35   $274.30  
  Purchase #6 $97.67   3.417%   $101.0074   $101.01   $101.00   $101.00  
  Purchase #7 $65.76   9.427%   $71.9592   $71.96   $71.95   $72.00  
  7 purchase totals = $800.74       $866.9422   $866.96   $866.95   $866.90