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 $212.94   10.283%   $234.8366   $234.84   $234.85   $234.80  
  Purchase #2 $91.37   4.466%   $95.4506   $95.45   $95.45   $95.50  
  Purchase #3 $25.49   6.697%   $27.1971   $27.20   $27.20   $27.20  
  Purchase #4 $126.78   9.444%   $138.7531   $138.75   $138.75   $138.80  
  Purchase #5 $131.66   8.216%   $142.4772   $142.48   $142.50   $142.50  
  Purchase #6 $247.33   13.310%   $280.2496   $280.25   $280.25   $280.20  
  Purchase #7 $58.92   8.574%   $63.9718   $63.97   $63.95   $64.00  
  7 purchase totals = $894.49       $982.9360   $982.94   $982.95   $983.00