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 $242.62   4.697%   $254.0159   $254.02   $254.00   $254.00  
  Purchase #2 $55.64   7.133%   $59.6088   $59.61   $59.60   $59.60  
  Purchase #3 $160.41   8.701%   $174.3673   $174.37   $174.35   $174.40  
  Purchase #4 $66.56   3.676%   $69.0067   $69.01   $69.00   $69.00  
  Purchase #5 $48.95   11.841%   $54.7462   $54.75   $54.75   $54.70  
  Purchase #6 $232.76   6.160%   $247.098   $247.10   $247.10   $247.10  
  Purchase #7 $135.25   9.597%   $148.2299   $148.23   $148.25   $148.20  
  7 purchase totals = $942.19       $1,007.0728   $1,007.09   $1,007.05   $1,007.00