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 $47.57   13.158%   $53.8293   $53.83   $53.85   $53.80  
  Purchase #2 $145.97   3.425%   $150.9695   $150.97   $150.95   $151.00  
  Purchase #3 $177.76   9.377%   $194.4286   $194.43   $194.45   $194.40  
  Purchase #4 $95.94   8.423%   $104.021   $104.02   $104.00   $104.00  
  Purchase #5 $234.52   5.398%   $247.1794   $247.18   $247.20   $247.20  
  Purchase #6 $26.90   3.466%   $27.8324   $27.83   $27.85   $27.80  
  Purchase #7 $125.62   11.218%   $139.7121   $139.71   $139.70   $139.70  
  7 purchase totals = $854.28       $917.9723   $917.97   $918.00   $917.90