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 $32.33   13.227%   $36.6063   $36.61   $36.60   $36.60  
  Purchase #2 $41.82   6.802%   $44.6646   $44.66   $44.65   $44.70  
  Purchase #3 $60.80   3.545%   $62.9554   $62.96   $62.95   $63.00  
  Purchase #4 $131.52   3.783%   $136.4954   $136.50   $136.50   $136.50  
  Purchase #5 $142.35   11.718%   $159.0306   $159.03   $159.05   $159.00  
  Purchase #6 $174.39   9.844%   $191.557   $191.56   $191.55   $191.60  
  Purchase #7 $212.86   6.709%   $227.1408   $227.14   $227.15   $227.10  
  7 purchase totals = $796.07       $858.4501   $858.46   $858.45   $858.50