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 $129.29   9.549%   $141.6359   $141.64   $141.65   $141.60  
  Purchase #2 $92.80   6.677%   $98.9963   $99.00   $99.00   $99.00  
  Purchase #3 $57.55   7.713%   $61.9888   $61.99   $62.00   $62.00  
  Purchase #4 $199.27   4.337%   $207.9123   $207.91   $207.90   $207.90  
  Purchase #5 $202.42   10.405%   $223.4818   $223.48   $223.50   $223.50  
  Purchase #6 $203.90   13.501%   $231.4285   $231.43   $231.45   $231.40  
  Purchase #7 $209.41   13.556%   $237.7976   $237.80   $237.80   $237.80  
  7 purchase totals = $1,094.64       $1,203.2412   $1,203.25   $1,203.30   $1,203.20