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 $198.74   13.614%   $225.7965   $225.80   $225.80   $225.80  
  Purchase #2 $32.86   4.465%   $34.3272   $34.33   $34.35   $34.30  
  Purchase #3 $91.84   4.134%   $95.6367   $95.64   $95.65   $95.60  
  Purchase #4 $204.71   7.500%   $220.0633   $220.06   $220.05   $220.10  
  Purchase #5 $110.50   8.125%   $119.4781   $119.48   $119.50   $119.50  
  Purchase #6 $79.68   9.387%   $87.1596   $87.16   $87.15   $87.20  
  Purchase #7 $132.84   10.752%   $147.123   $147.12   $147.10   $147.10  
  7 purchase totals = $851.17       $929.5844   $929.59   $929.60   $929.60