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 $60.76   6.194%   $64.5235   $64.52   $64.50   $64.50  
  Purchase #2 $236.91   11.817%   $264.9057   $264.91   $264.90   $264.90  
  Purchase #3 $81.25   3.804%   $84.3408   $84.34   $84.35   $84.30  
  Purchase #4 $5.26   4.405%   $5.4917   $5.49   $5.50   $5.50  
  Purchase #5 $241.96   9.592%   $265.1688   $265.17   $265.15   $265.20  
  Purchase #6 $203.52   10.619%   $225.1318   $225.13   $225.15   $225.10  
  Purchase #7 $120.35   3.249%   $124.2602   $124.26   $124.25   $124.30  
  7 purchase totals = $950.01       $1,033.8225   $1,033.82   $1,033.80   $1,033.80