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 $212.85   11.349%   $237.0063   $237.01   $237.00   $237.00  
  Purchase #2 $60.88   3.145%   $62.7947   $62.79   $62.80   $62.80  
  Purchase #3 $167.68   6.374%   $178.3679   $178.37   $178.35   $178.40  
  Purchase #4 $63.64   6.283%   $67.6385   $67.64   $67.65   $67.60  
  Purchase #5 $186.98   5.817%   $197.8566   $197.86   $197.85   $197.90  
  Purchase #6 $9.65   5.487%   $10.1795   $10.18   $10.20   $10.20  
  Purchase #7 $36.39   13.522%   $41.3107   $41.31   $41.30   $41.30  
  7 purchase totals = $738.07       $795.1542   $795.16   $795.15   $795.20