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 $227.62   7.552%   $244.8099   $244.81   $244.80   $244.80  
  Purchase #2 $68.60   6.353%   $72.9582   $72.96   $72.95   $73.00  
  Purchase #3 $148.93   11.133%   $165.5104   $165.51   $165.50   $165.50  
  Purchase #4 $105.84   12.626%   $119.2034   $119.20   $119.20   $119.20  
  Purchase #5 $228.29   8.141%   $246.8751   $246.88   $246.90   $246.90  
  Purchase #6 $159.49   13.581%   $181.1503   $181.15   $181.15   $181.20  
  Purchase #7 $12.80   11.486%   $14.2702   $14.27   $14.25   $14.30  
  7 purchase totals = $951.57       $1,044.7775   $1,044.78   $1,044.75   $1,044.90