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 $210.63   9.747%   $231.1601   $231.16   $231.15   $231.20  
  Purchase #2 $36.32   9.744%   $39.859   $39.86   $39.85   $39.90  
  Purchase #3 $127.85   8.870%   $139.1903   $139.19   $139.20   $139.20  
  Purchase #4 $216.38   12.388%   $243.1852   $243.19   $243.20   $243.20  
  Purchase #5 $129.90   4.792%   $136.1248   $136.12   $136.10   $136.10  
  Purchase #6 $88.88   12.214%   $99.7358   $99.74   $99.75   $99.70  
  Purchase #7 $111.57   7.642%   $120.0962   $120.10   $120.10   $120.10  
  7 purchase totals = $921.53       $1,009.3514   $1,009.36   $1,009.35   $1,009.40