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 $60.55   9.297%   $66.1793   $66.18   $66.20   $66.20  
  Purchase #2 $32.85   3.425%   $33.9751   $33.98   $34.00   $34.00  
  Purchase #3 $173.70   5.721%   $183.6374   $183.64   $183.65   $183.60  
  Purchase #4 $223.63   6.831%   $238.9062   $238.91   $238.90   $238.90  
  Purchase #5 $61.74   4.243%   $64.3596   $64.36   $64.35   $64.40  
  Purchase #6 $182.68   10.593%   $202.0313   $202.03   $202.05   $202.00  
  Purchase #7 $136.52   9.502%   $149.4921   $149.49   $149.50   $149.50  
  7 purchase totals = $871.67       $938.5810   $938.59   $938.65   $938.60