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 $248.33   5.782%   $262.6884   $262.69   $262.70   $262.70  
  Purchase #2 $158.93   8.214%   $171.9845   $171.98   $172.00   $172.00  
  Purchase #3 $125.34   10.513%   $138.517   $138.52   $138.50   $138.50  
  Purchase #4 $92.42   9.651%   $101.3395   $101.34   $101.35   $101.30  
  Purchase #5 $60.48   3.343%   $62.5018   $62.50   $62.50   $62.50  
  Purchase #6 $152.94   4.739%   $160.1878   $160.19   $160.20   $160.20  
  Purchase #7 $154.53   12.135%   $173.2822   $173.28   $173.30   $173.30  
  7 purchase totals = $992.97       $1,070.5012   $1,070.50   $1,070.55   $1,070.50