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 $232.82   4.583%   $243.4901   $243.49   $243.50   $243.50  
  Purchase #2 $145.56   9.366%   $159.1931   $159.19   $159.20   $159.20  
  Purchase #3 $221.92   6.551%   $236.458   $236.46   $236.45   $236.50  
  Purchase #4 $167.45   8.221%   $181.2161   $181.22   $181.20   $181.20  
  Purchase #5 $91.59   7.179%   $98.1652   $98.17   $98.15   $98.20  
  Purchase #6 $48.29   5.116%   $50.7605   $50.76   $50.75   $50.80  
  Purchase #7 $52.50   5.443%   $55.3576   $55.36   $55.35   $55.40  
  7 purchase totals = $960.13       $1,024.6406   $1,024.65   $1,024.60   $1,024.80