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 $53.55   11.285%   $59.5931   $59.59   $59.60   $59.60  
  Purchase #2 $44.89   7.104%   $48.079   $48.08   $48.10   $48.10  
  Purchase #3 $48.29   13.486%   $54.8024   $54.80   $54.80   $54.80  
  Purchase #4 $19.85   11.194%   $22.072   $22.07   $22.05   $22.10  
  Purchase #5 $52.95   6.480%   $56.3812   $56.38   $56.40   $56.40  
  Purchase #6 $191.57   8.385%   $207.6331   $207.63   $207.65   $207.60  
  Purchase #7 $12.96   13.588%   $14.721   $14.72   $14.70   $14.70  
  7 purchase totals = $424.06       $463.2818   $463.27   $463.30   $463.30