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 $56.96   8.414%   $61.7526   $61.75   $61.75   $61.80  
  Purchase #2 $133.92   9.224%   $146.2728   $146.27   $146.25   $146.30  
  Purchase #3 $244.92   9.140%   $267.3057   $267.31   $267.30   $267.30  
  Purchase #4 $207.53   6.846%   $221.7375   $221.74   $221.75   $221.70  
  Purchase #5 $217.82   10.641%   $240.9982   $241.00   $241.00   $241.00  
  Purchase #6 $207.62   11.376%   $231.2389   $231.24   $231.25   $231.20  
  Purchase #7 $39.65   4.774%   $41.5429   $41.54   $41.55   $41.50  
  7 purchase totals = $1,108.42       $1,210.8486   $1,210.85   $1,210.85   $1,210.80