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 $181.93   10.336%   $200.7343   $200.73   $200.75   $200.70  
  Purchase #2 $243.62   7.578%   $262.0815   $262.08   $262.10   $262.10  
  Purchase #3 $119.36   10.244%   $131.5872   $131.59   $131.60   $131.60  
  Purchase #4 $29.43   13.344%   $33.3571   $33.36   $33.35   $33.40  
  Purchase #5 $236.82   4.722%   $248.0026   $248.00   $248.00   $248.00  
  Purchase #6 $222.36   12.549%   $250.264   $250.26   $250.25   $250.30  
  Purchase #7 $82.62   7.237%   $88.5992   $88.60   $88.60   $88.60  
  7 purchase totals = $1,116.14       $1,214.6259   $1,214.62   $1,214.65   $1,214.70