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 $230.81   5.271%   $242.976   $242.98   $243.00   $243.00  
  Purchase #2 $65.80   5.687%   $69.542   $69.54   $69.55   $69.50  
  Purchase #3 $70.65   6.569%   $75.291   $75.29   $75.30   $75.30  
  Purchase #4 $84.54   4.464%   $88.3139   $88.31   $88.30   $88.30  
  Purchase #5 $229.40   11.430%   $255.6204   $255.62   $255.60   $255.60  
  Purchase #6 $36.26   13.774%   $41.2545   $41.25   $41.25   $41.30  
  Purchase #7 $170.69   5.596%   $180.2418   $180.24   $180.25   $180.20  
  7 purchase totals = $888.15       $953.2396   $953.23   $953.25   $953.20