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 $59.61   7.214%   $63.9103   $63.91   $63.90   $63.90  
  Purchase #2 $49.35   3.183%   $50.9208   $50.92   $50.90   $50.90  
  Purchase #3 $74.59   5.755%   $78.8827   $78.88   $78.90   $78.90  
  Purchase #4 $50.68   3.727%   $52.5688   $52.57   $52.55   $52.60  
  Purchase #5 $219.77   7.369%   $235.9649   $235.96   $235.95   $236.00  
  Purchase #6 $195.72   10.564%   $216.3959   $216.40   $216.40   $216.40  
  Purchase #7 $244.58   7.805%   $263.6695   $263.67   $263.65   $263.70  
  7 purchase totals = $894.30       $962.3129   $962.31   $962.25   $962.40