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 $68.96   6.129%   $73.1866   $73.19   $73.20   $73.20  
  Purchase #2 $10.26   9.515%   $11.2362   $11.24   $11.25   $11.20  
  Purchase #3 $216.44   6.557%   $230.632   $230.63   $230.65   $230.60  
  Purchase #4 $241.85   9.395%   $264.5718   $264.57   $264.55   $264.60  
  Purchase #5 $37.95   4.544%   $39.6744   $39.67   $39.65   $39.70  
  Purchase #6 $118.41   5.706%   $125.1665   $125.17   $125.15   $125.20  
  Purchase #7 $8.30   4.593%   $8.6812   $8.68   $8.70   $8.70  
  7 purchase totals = $702.17       $753.1487   $753.15   $753.15   $753.20