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 $52.53   10.497%   $58.0441   $58.04   $58.05   $58.00  
  Purchase #2 $33.97   6.381%   $36.1376   $36.14   $36.15   $36.10  
  Purchase #3 $165.88   7.829%   $178.8667   $178.87   $178.85   $178.90  
  Purchase #4 $111.31   6.762%   $118.8368   $118.84   $118.85   $118.80  
  Purchase #5 $33.88   9.653%   $37.1504   $37.15   $37.15   $37.20  
  Purchase #6 $173.81   11.615%   $193.998   $194.00   $194.00   $194.00  
  Purchase #7 $246.49   11.827%   $275.6424   $275.64   $275.65   $275.60  
  7 purchase totals = $817.87       $898.6760   $898.68   $898.70   $898.60