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 $232.61   13.620%   $264.2915   $264.29   $264.30   $264.30  
  Purchase #2 $71.62   3.809%   $74.348   $74.35   $74.35   $74.30  
  Purchase #3 $20.65   7.685%   $22.237   $22.24   $22.25   $22.20  
  Purchase #4 $5.77   4.171%   $6.0107   $6.01   $6.00   $6.00  
  Purchase #5 $194.88   5.131%   $204.8793   $204.88   $204.90   $204.90  
  Purchase #6 $119.29   5.427%   $125.7639   $125.76   $125.75   $125.80  
  Purchase #7 $185.69   4.812%   $194.6254   $194.63   $194.65   $194.60  
  7 purchase totals = $830.51       $892.1558   $892.16   $892.20   $892.10