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 $53.62   6.763%   $57.2463   $57.25   $57.25   $57.20  
  Purchase #2 $80.43   4.282%   $83.874   $83.87   $83.85   $83.90  
  Purchase #3 $177.69   9.196%   $194.0304   $194.03   $194.05   $194.00  
  Purchase #4 $85.47   10.365%   $94.329   $94.33   $94.35   $94.30  
  Purchase #5 $63.30   12.122%   $70.9732   $70.97   $70.95   $71.00  
  Purchase #6 $239.80   8.817%   $260.9432   $260.94   $260.95   $260.90  
  Purchase #7 $241.33   9.608%   $264.517   $264.52   $264.50   $264.50  
  7 purchase totals = $941.64       $1,025.9131   $1,025.91   $1,025.90   $1,025.80