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 $188.82   6.493%   $201.0801   $201.08   $201.10   $201.10  
  Purchase #2 $152.95   7.818%   $164.9076   $164.91   $164.90   $164.90  
  Purchase #3 $58.60   11.393%   $65.2763   $65.28   $65.30   $65.30  
  Purchase #4 $21.34   4.775%   $22.359   $22.36   $22.35   $22.40  
  Purchase #5 $149.64   9.802%   $164.3077   $164.31   $164.30   $164.30  
  Purchase #6 $183.75   6.494%   $195.6827   $195.68   $195.70   $195.70  
  Purchase #7 $22.52   3.180%   $23.2361   $23.24   $23.25   $23.20  
  7 purchase totals = $777.62       $836.8495   $836.86   $836.90   $836.90