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 $53.51   13.451%   $60.7076   $60.71   $60.70   $60.70  
  Purchase #2 $56.96   4.714%   $59.6451   $59.65   $59.65   $59.60  
  Purchase #3 $84.88   4.510%   $88.7081   $88.71   $88.70   $88.70  
  Purchase #4 $70.34   4.143%   $73.2542   $73.25   $73.25   $73.30  
  Purchase #5 $8.70   11.453%   $9.6964   $9.70   $9.70   $9.70  
  Purchase #6 $6.55   13.373%   $7.4259   $7.43   $7.45   $7.40  
  Purchase #7 $156.80   13.412%   $177.83   $177.83   $177.85   $177.80  
  7 purchase totals = $437.74       $477.2673   $477.28   $477.30   $477.20