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 $220.71   11.299%   $245.648   $245.65   $245.65   $245.60  
  Purchase #2 $169.63   11.310%   $188.8152   $188.82   $188.80   $188.80  
  Purchase #3 $195.26   10.598%   $215.9537   $215.95   $215.95   $216.00  
  Purchase #4 $174.66   12.855%   $197.1125   $197.11   $197.10   $197.10  
  Purchase #5 $5.48   9.552%   $6.0034   $6.00   $6.00   $6.00  
  Purchase #6 $121.62   3.162%   $125.4656   $125.47   $125.45   $125.50  
  Purchase #7 $32.62   3.796%   $33.8583   $33.86   $33.85   $33.90  
  7 purchase totals = $919.98       $1,012.8567   $1,012.86   $1,012.80   $1,012.90