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 $58.98   6.776%   $62.9765   $62.98   $63.00   $63.00  
  Purchase #2 $113.65   4.241%   $118.4699   $118.47   $118.45   $118.50  
  Purchase #3 $113.64   4.280%   $118.5038   $118.50   $118.50   $118.50  
  Purchase #4 $123.82   4.430%   $129.3052   $129.31   $129.30   $129.30  
  Purchase #5 $41.87   6.211%   $44.4705   $44.47   $44.45   $44.50  
  Purchase #6 $150.68   10.692%   $166.7907   $166.79   $166.80   $166.80  
  Purchase #7 $154.81   6.249%   $164.4841   $164.48   $164.50   $164.50  
  7 purchase totals = $757.45       $805.0007   $805.00   $805.00   $805.10