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 $207.46   13.659%   $235.797   $235.80   $235.80   $235.80  
  Purchase #2 $77.86   12.604%   $87.6735   $87.67   $87.65   $87.70  
  Purchase #3 $114.36   10.857%   $126.7761   $126.78   $126.80   $126.80  
  Purchase #4 $85.61   7.387%   $91.934   $91.93   $91.95   $91.90  
  Purchase #5 $182.89   9.769%   $200.7565   $200.76   $200.75   $200.80  
  Purchase #6 $20.77   5.255%   $21.8615   $21.86   $21.85   $21.90  
  Purchase #7 $245.67   10.300%   $270.974   $270.97   $270.95   $271.00  
  7 purchase totals = $934.62       $1,035.7726   $1,035.77   $1,035.75   $1,035.90