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 $85.38   8.315%   $92.4793   $92.48   $92.50   $92.50  
  Purchase #2 $124.62   10.434%   $137.6229   $137.62   $137.60   $137.60  
  Purchase #3 $110.30   13.653%   $125.3593   $125.36   $125.35   $125.40  
  Purchase #4 $39.94   3.748%   $41.437   $41.44   $41.45   $41.40  
  Purchase #5 $213.47   5.480%   $225.1682   $225.17   $225.15   $225.20  
  Purchase #6 $179.27   13.436%   $203.3567   $203.36   $203.35   $203.40  
  Purchase #7 $171.59   6.651%   $183.0025   $183.00   $183.00   $183.00  
  7 purchase totals = $924.57       $1,008.4259   $1,008.43   $1,008.40   $1,008.50