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 $114.29   12.167%   $128.1957   $128.20   $128.20   $128.20  
  Purchase #2 $245.79   11.463%   $273.9649   $273.96   $273.95   $274.00  
  Purchase #3 $126.89   8.264%   $137.3762   $137.38   $137.40   $137.40  
  Purchase #4 $183.92   11.263%   $204.6349   $204.63   $204.65   $204.60  
  Purchase #5 $231.44   7.855%   $249.6196   $249.62   $249.60   $249.60  
  Purchase #6 $127.66   5.312%   $134.4413   $134.44   $134.45   $134.40  
  Purchase #7 $5.59   9.342%   $6.1122   $6.11   $6.10   $6.10  
  7 purchase totals = $1,035.58       $1,134.3448   $1,134.34   $1,134.35   $1,134.30