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 $16.35   12.325%   $18.3651   $18.37   $18.35   $18.40  
  Purchase #2 $151.30   5.814%   $160.0966   $160.10   $160.10   $160.10  
  Purchase #3 $50.86   4.638%   $53.2189   $53.22   $53.20   $53.20  
  Purchase #4 $20.80   8.440%   $22.5555   $22.56   $22.55   $22.60  
  Purchase #5 $152.65   4.551%   $159.5971   $159.60   $159.60   $159.60  
  Purchase #6 $228.42   3.343%   $236.0561   $236.06   $236.05   $236.10  
  Purchase #7 $152.34   9.783%   $167.2434   $167.24   $167.25   $167.20  
  7 purchase totals = $772.72       $817.1327   $817.15   $817.10   $817.20