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 $113.40   5.126%   $119.2129   $119.21   $119.20   $119.20  
  Purchase #2 $196.82   10.521%   $217.5274   $217.53   $217.55   $217.50  
  Purchase #3 $210.75   3.849%   $218.8618   $218.86   $218.85   $218.90  
  Purchase #4 $160.86   3.814%   $166.9952   $167.00   $167.00   $167.00  
  Purchase #5 $216.49   6.141%   $229.7847   $229.78   $229.80   $229.80  
  Purchase #6 $42.85   12.324%   $48.1308   $48.13   $48.15   $48.10  
  Purchase #7 $11.82   6.308%   $12.5656   $12.57   $12.55   $12.60  
  7 purchase totals = $952.99       $1,013.0784   $1,013.08   $1,013.10   $1,013.10