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 $241.85   10.572%   $267.4184   $267.42   $267.40   $267.40  
  Purchase #2 $110.27   11.640%   $123.1054   $123.11   $123.10   $123.10  
  Purchase #3 $190.27   8.868%   $207.1431   $207.14   $207.15   $207.10  
  Purchase #4 $173.71   9.310%   $189.8824   $189.88   $189.90   $189.90  
  Purchase #5 $96.88   13.659%   $110.1128   $110.11   $110.10   $110.10  
  Purchase #6 $64.58   9.345%   $70.615   $70.62   $70.60   $70.60  
  Purchase #7 $81.56   12.763%   $91.9695   $91.97   $91.95   $92.00  
  7 purchase totals = $959.12       $1,060.2466   $1,060.25   $1,060.20   $1,060.20