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 $69.74   8.293%   $75.5235   $75.52   $75.50   $75.50  
  Purchase #2 $196.95   3.846%   $204.5247   $204.52   $204.50   $204.50  
  Purchase #3 $32.82   11.280%   $36.5221   $36.52   $36.50   $36.50  
  Purchase #4 $24.27   6.222%   $25.7801   $25.78   $25.80   $25.80  
  Purchase #5 $169.62   3.597%   $175.7212   $175.72   $175.70   $175.70  
  Purchase #6 $44.28   6.361%   $47.0967   $47.10   $47.10   $47.10  
  Purchase #7 $229.37   9.350%   $250.8161   $250.82   $250.80   $250.80  
  7 purchase totals = $767.05       $815.9844   $815.98   $815.90   $815.90