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 $58.35   10.310%   $64.3659   $64.37   $64.35   $64.40  
  Purchase #2 $195.66   4.605%   $204.6701   $204.67   $204.65   $204.70  
  Purchase #3 $168.33   9.187%   $183.7945   $183.79   $183.80   $183.80  
  Purchase #4 $95.98   13.403%   $108.8442   $108.84   $108.85   $108.80  
  Purchase #5 $181.64   11.726%   $202.9391   $202.94   $202.95   $202.90  
  Purchase #6 $159.26   7.144%   $170.6375   $170.64   $170.65   $170.60  
  Purchase #7 $25.55   6.185%   $27.1303   $27.13   $27.15   $27.10  
  7 purchase totals = $884.77       $962.3816   $962.38   $962.40   $962.30