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 $159.63   4.829%   $167.3385   $167.34   $167.35   $167.30  
  Purchase #2 $101.44   11.746%   $113.3551   $113.36   $113.35   $113.40  
  Purchase #3 $29.64   11.411%   $33.0222   $33.02   $33.00   $33.00  
  Purchase #4 $53.55   3.427%   $55.3852   $55.39   $55.40   $55.40  
  Purchase #5 $95.59   3.316%   $98.7598   $98.76   $98.75   $98.80  
  Purchase #6 $197.25   3.202%   $203.5659   $203.57   $203.55   $203.60  
  Purchase #7 $20.53   9.694%   $22.5202   $22.52   $22.50   $22.50  
  7 purchase totals = $657.63       $693.9469   $693.96   $693.90   $694.00