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 $160.54   13.223%   $181.7682   $181.77   $181.75   $181.80  
  Purchase #2 $122.80   6.436%   $130.7034   $130.70   $130.70   $130.70  
  Purchase #3 $119.97   12.209%   $134.6171   $134.62   $134.60   $134.60  
  Purchase #4 $239.35   6.783%   $255.5851   $255.59   $255.60   $255.60  
  Purchase #5 $241.32   7.123%   $258.5092   $258.51   $258.50   $258.50  
  Purchase #6 $205.44   10.506%   $227.0235   $227.02   $227.00   $227.00  
  Purchase #7 $12.45   11.804%   $13.9196   $13.92   $13.90   $13.90  
  7 purchase totals = $1,101.87       $1,202.1261   $1,202.13   $1,202.05   $1,202.10