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 $176.94   12.379%   $198.8434   $198.84   $198.85   $198.80  
  Purchase #2 $147.32   6.523%   $156.9297   $156.93   $156.95   $156.90  
  Purchase #3 $58.72   7.732%   $63.2602   $63.26   $63.25   $63.30  
  Purchase #4 $159.33   7.159%   $170.7364   $170.74   $170.75   $170.70  
  Purchase #5 $164.82   13.361%   $186.8416   $186.84   $186.85   $186.80  
  Purchase #6 $164.65   5.317%   $173.4044   $173.40   $173.40   $173.40  
  Purchase #7 $86.56   7.389%   $92.9559   $92.96   $92.95   $93.00  
  7 purchase totals = $958.34       $1,042.9716   $1,042.97   $1,043.00   $1,042.90