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 $236.96   13.227%   $268.3027   $268.30   $268.30   $268.30  
  Purchase #2 $77.69   4.526%   $81.2062   $81.21   $81.20   $81.20  
  Purchase #3 $75.35   6.548%   $80.2839   $80.28   $80.30   $80.30  
  Purchase #4 $229.91   6.336%   $244.4771   $244.48   $244.50   $244.50  
  Purchase #5 $246.92   10.264%   $272.2639   $272.26   $272.25   $272.30  
  Purchase #6 $140.54   3.316%   $145.2003   $145.20   $145.20   $145.20  
  Purchase #7 $10.82   11.484%   $12.0626   $12.06   $12.05   $12.10  
  7 purchase totals = $1,018.19       $1,103.7967   $1,103.79   $1,103.80   $1,103.90