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 $25.80   5.764%   $27.2871   $27.29   $27.30   $27.30  
  Purchase #2 $160.99   3.532%   $166.6762   $166.68   $166.70   $166.70  
  Purchase #3 $233.55   5.722%   $246.9137   $246.91   $246.90   $246.90  
  Purchase #4 $93.93   3.298%   $97.0278   $97.03   $97.05   $97.00  
  Purchase #5 $107.91   6.618%   $115.0515   $115.05   $115.05   $115.10  
  Purchase #6 $11.75   5.181%   $12.3588   $12.36   $12.35   $12.40  
  Purchase #7 $71.78   3.277%   $74.1322   $74.13   $74.15   $74.10  
  7 purchase totals = $705.71       $739.4473   $739.45   $739.50   $739.50