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 $47.86   8.630%   $51.9903   $51.99   $52.00   $52.00  
  Purchase #2 $186.93   4.737%   $195.7849   $195.78   $195.80   $195.80  
  Purchase #3 $148.64   3.394%   $153.6848   $153.68   $153.70   $153.70  
  Purchase #4 $41.87   11.415%   $46.6495   $46.65   $46.65   $46.60  
  Purchase #5 $71.68   11.716%   $80.078   $80.08   $80.10   $80.10  
  Purchase #6 $32.59   4.189%   $33.9552   $33.96   $33.95   $34.00  
  Purchase #7 $26.65   9.535%   $29.1911   $29.19   $29.20   $29.20  
  7 purchase totals = $556.22       $591.3338   $591.33   $591.40   $591.40