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 $65.87   5.263%   $69.3367   $69.34   $69.35   $69.30  
  Purchase #2 $71.92   11.284%   $80.0355   $80.04   $80.05   $80.00  
  Purchase #3 $195.74   12.318%   $219.8513   $219.85   $219.85   $219.90  
  Purchase #4 $11.75   13.166%   $13.297   $13.30   $13.30   $13.30  
  Purchase #5 $246.93   5.410%   $260.2889   $260.29   $260.30   $260.30  
  Purchase #6 $95.49   3.610%   $98.9372   $98.94   $98.95   $98.90  
  Purchase #7 $17.49   11.103%   $19.4319   $19.43   $19.45   $19.40  
  7 purchase totals = $705.19       $761.1785   $761.19   $761.25   $761.10