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 $11.39   11.304%   $12.6775   $12.68   $12.70   $12.70  
  Purchase #2 $78.29   12.504%   $88.0794   $88.08   $88.10   $88.10  
  Purchase #3 $93.57   8.333%   $101.3672   $101.37   $101.35   $101.40  
  Purchase #4 $227.59   11.371%   $253.4693   $253.47   $253.45   $253.50  
  Purchase #5 $9.39   13.739%   $10.6801   $10.68   $10.70   $10.70  
  Purchase #6 $91.42   5.760%   $96.6858   $96.69   $96.70   $96.70  
  Purchase #7 $130.97   6.570%   $139.5747   $139.57   $139.55   $139.60  
  7 purchase totals = $642.62       $702.5340   $702.54   $702.55   $702.70