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 $245.49   11.766%   $274.3744   $274.37   $274.35   $274.40  
  Purchase #2 $220.93   6.516%   $235.3258   $235.33   $235.35   $235.30  
  Purchase #3 $139.39   11.540%   $155.4756   $155.48   $155.50   $155.50  
  Purchase #4 $96.56   10.551%   $106.748   $106.75   $106.75   $106.70  
  Purchase #5 $240.53   11.592%   $268.4122   $268.41   $268.40   $268.40  
  Purchase #6 $85.72   7.434%   $92.0924   $92.09   $92.10   $92.10  
  Purchase #7 $241.56   13.663%   $274.5643   $274.56   $274.55   $274.60  
  7 purchase totals = $1,270.18       $1,406.9927   $1,406.99   $1,407.00   $1,407.00