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 $245.89   6.801%   $262.613   $262.61   $262.60   $262.60  
  Purchase #2 $80.70   10.427%   $89.1146   $89.11   $89.10   $89.10  
  Purchase #3 $201.28   9.322%   $220.0433   $220.04   $220.05   $220.00  
  Purchase #4 $86.94   6.369%   $92.4772   $92.48   $92.50   $92.50  
  Purchase #5 $117.74   7.606%   $126.6953   $126.70   $126.70   $126.70  
  Purchase #6 $118.43   12.819%   $133.6115   $133.61   $133.60   $133.60  
  Purchase #7 $43.48   3.854%   $45.1557   $45.16   $45.15   $45.20  
  7 purchase totals = $894.46       $969.7106   $969.71   $969.70   $969.70