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 $203.95   11.203%   $226.7985   $226.80   $226.80   $226.80  
  Purchase #2 $5.34   13.139%   $6.0416   $6.04   $6.05   $6.00  
  Purchase #3 $141.53   4.552%   $147.9724   $147.97   $147.95   $148.00  
  Purchase #4 $62.43   7.714%   $67.2459   $67.25   $67.25   $67.20  
  Purchase #5 $88.51   3.169%   $91.3149   $91.31   $91.30   $91.30  
  Purchase #6 $218.35   7.833%   $235.4534   $235.45   $235.45   $235.50  
  Purchase #7 $231.37   10.408%   $255.451   $255.45   $255.45   $255.50  
  7 purchase totals = $951.48       $1,030.2777   $1,030.27   $1,030.25   $1,030.30