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 $123.26   8.697%   $133.9799   $133.98   $134.00   $134.00  
  Purchase #2 $179.45   11.328%   $199.7781   $199.78   $199.80   $199.80  
  Purchase #3 $33.25   10.212%   $36.6455   $36.65   $36.65   $36.60  
  Purchase #4 $215.78   5.806%   $228.3082   $228.31   $228.30   $228.30  
  Purchase #5 $250.86   9.361%   $274.343   $274.34   $274.35   $274.30  
  Purchase #6 $124.93   8.289%   $135.2854   $135.29   $135.30   $135.30  
  Purchase #7 $23.95   8.274%   $25.9316   $25.93   $25.95   $25.90  
  7 purchase totals = $951.48       $1,034.2717   $1,034.28   $1,034.35   $1,034.20