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 $242.96   10.516%   $268.5097   $268.51   $268.50   $268.50  
  Purchase #2 $109.54   13.687%   $124.5327   $124.53   $124.55   $124.50  
  Purchase #3 $138.47   10.668%   $153.242   $153.24   $153.25   $153.20  
  Purchase #4 $94.67   6.652%   $100.9674   $100.97   $100.95   $101.00  
  Purchase #5 $161.76   10.775%   $179.1896   $179.19   $179.20   $179.20  
  Purchase #6 $171.36   13.296%   $194.144   $194.14   $194.15   $194.10  
  Purchase #7 $39.52   11.871%   $44.2114   $44.21   $44.20   $44.20  
  7 purchase totals = $958.28       $1,064.7968   $1,064.79   $1,064.80   $1,064.70