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 $60.45   12.133%   $67.7844   $67.78   $67.80   $67.80  
  Purchase #2 $94.50   13.453%   $107.2131   $107.21   $107.20   $107.20  
  Purchase #3 $112.43   6.575%   $119.8223   $119.82   $119.80   $119.80  
  Purchase #4 $234.31   6.705%   $250.0205   $250.02   $250.00   $250.00  
  Purchase #5 $118.83   3.689%   $123.2136   $123.21   $123.20   $123.20  
  Purchase #6 $183.29   12.163%   $205.5836   $205.58   $205.60   $205.60  
  Purchase #7 $19.96   12.601%   $22.4752   $22.48   $22.50   $22.50  
  7 purchase totals = $823.77       $896.1127   $896.10   $896.10   $896.10