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 $67.75   10.636%   $74.9559   $74.96   $74.95   $75.00  
  Purchase #2 $106.98   6.429%   $113.8577   $113.86   $113.85   $113.90  
  Purchase #3 $207.61   5.445%   $218.9144   $218.91   $218.90   $218.90  
  Purchase #4 $199.72   9.405%   $218.5037   $218.50   $218.50   $218.50  
  Purchase #5 $242.55   6.270%   $257.7579   $257.76   $257.75   $257.80  
  Purchase #6 $72.29   3.251%   $74.6401   $74.64   $74.65   $74.60  
  Purchase #7 $36.55   9.809%   $40.1352   $40.14   $40.15   $40.10  
  7 purchase totals = $933.45       $998.7649   $998.77   $998.75   $998.80