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 $143.34   6.855%   $153.166   $153.17   $153.15   $153.20  
  Purchase #2 $55.65   9.601%   $60.993   $60.99   $61.00   $61.00  
  Purchase #3 $178.98   6.587%   $190.7694   $190.77   $190.75   $190.80  
  Purchase #4 $242.55   5.638%   $256.225   $256.23   $256.25   $256.20  
  Purchase #5 $111.45   12.700%   $125.6042   $125.60   $125.60   $125.60  
  Purchase #6 $22.93   13.733%   $26.079   $26.08   $26.10   $26.10  
  Purchase #7 $188.35   12.701%   $212.2723   $212.27   $212.25   $212.30  
  7 purchase totals = $943.25       $1,025.1089   $1,025.11   $1,025.10   $1,025.20