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 $226.45   11.823%   $253.2232   $253.22   $253.20   $253.20  
  Purchase #2 $62.49   10.241%   $68.8896   $68.89   $68.90   $68.90  
  Purchase #3 $171.84   10.542%   $189.9554   $189.96   $189.95   $190.00  
  Purchase #4 $48.98   8.813%   $53.2966   $53.30   $53.30   $53.30  
  Purchase #5 $24.44   7.827%   $26.3529   $26.35   $26.35   $26.40  
  Purchase #6 $209.83   6.330%   $223.1122   $223.11   $223.10   $223.10  
  Purchase #7 $181.34   7.590%   $195.1037   $195.10   $195.10   $195.10  
  7 purchase totals = $925.37       $1,009.9336   $1,009.93   $1,009.90   $1,010.00