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 $63.46   12.618%   $71.4674   $71.47   $71.45   $71.50  
  Purchase #2 $203.32   3.130%   $209.6839   $209.68   $209.70   $209.70  
  Purchase #3 $160.28   5.783%   $169.549   $169.55   $169.55   $169.50  
  Purchase #4 $129.97   7.202%   $139.3304   $139.33   $139.35   $139.30  
  Purchase #5 $158.33   3.175%   $163.357   $163.36   $163.35   $163.40  
  Purchase #6 $94.98   11.590%   $105.9882   $105.99   $106.00   $106.00  
  Purchase #7 $138.39   3.395%   $143.0883   $143.09   $143.10   $143.10  
  7 purchase totals = $948.73       $1,002.4642   $1,002.47   $1,002.50   $1,002.50