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 $191.74   6.206%   $203.6394   $203.64   $203.65   $203.60  
  Purchase #2 $198.76   7.117%   $212.9057   $212.91   $212.90   $212.90  
  Purchase #3 $250.36   8.622%   $271.946   $271.95   $271.95   $271.90  
  Purchase #4 $209.80   11.764%   $234.4809   $234.48   $234.50   $234.50  
  Purchase #5 $48.60   13.240%   $55.0346   $55.03   $55.05   $55.00  
  Purchase #6 $68.51   9.613%   $75.0959   $75.10   $75.10   $75.10  
  Purchase #7 $207.56   5.488%   $218.9509   $218.95   $218.95   $219.00  
  7 purchase totals = $1,175.33       $1,272.0534   $1,272.06   $1,272.10   $1,272.00