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 $192.51   5.803%   $203.6814   $203.68   $203.70   $203.70  
  Purchase #2 $165.43   12.814%   $186.6282   $186.63   $186.65   $186.60  
  Purchase #3 $231.88   10.601%   $256.4616   $256.46   $256.45   $256.50  
  Purchase #4 $94.72   10.631%   $104.7897   $104.79   $104.80   $104.80  
  Purchase #5 $53.73   12.646%   $60.5247   $60.52   $60.50   $60.50  
  Purchase #6 $87.36   13.399%   $99.0654   $99.07   $99.05   $99.10  
  Purchase #7 $235.36   12.739%   $265.3425   $265.34   $265.35   $265.30  
  7 purchase totals = $1,060.99       $1,176.4935   $1,176.49   $1,176.50   $1,176.50