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 $183.38   11.633%   $204.7126   $204.71   $204.70   $204.70  
  Purchase #2 $137.62   10.573%   $152.1706   $152.17   $152.15   $152.20  
  Purchase #3 $46.96   3.865%   $48.775   $48.78   $48.80   $48.80  
  Purchase #4 $141.72   8.305%   $153.4898   $153.49   $153.50   $153.50  
  Purchase #5 $177.86   6.637%   $189.6646   $189.66   $189.65   $189.70  
  Purchase #6 $36.31   8.434%   $39.3724   $39.37   $39.35   $39.40  
  Purchase #7 $56.47   13.363%   $64.0161   $64.02   $64.00   $64.00  
  7 purchase totals = $780.32       $852.2011   $852.20   $852.15   $852.30