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 $205.79   12.756%   $232.0406   $232.04   $232.05   $232.00  
  Purchase #2 $147.53   13.874%   $167.9983   $168.00   $168.00   $168.00  
  Purchase #3 $29.90   11.337%   $33.2898   $33.29   $33.30   $33.30  
  Purchase #4 $217.73   8.375%   $235.9649   $235.96   $235.95   $236.00  
  Purchase #5 $171.27   5.472%   $180.6419   $180.64   $180.65   $180.60  
  Purchase #6 $85.35   13.361%   $96.7536   $96.75   $96.75   $96.80  
  Purchase #7 $116.89   9.418%   $127.8987   $127.90   $127.90   $127.90  
  7 purchase totals = $974.46       $1,074.5878   $1,074.58   $1,074.60   $1,074.60