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 $5.59   13.531%   $6.3464   $6.35   $6.35   $6.30  
  Purchase #2 $34.86   7.195%   $37.3682   $37.37   $37.35   $37.40  
  Purchase #3 $208.37   9.411%   $227.9797   $227.98   $228.00   $228.00  
  Purchase #4 $223.39   11.829%   $249.8148   $249.81   $249.80   $249.80  
  Purchase #5 $31.69   3.821%   $32.9009   $32.90   $32.90   $32.90  
  Purchase #6 $167.56   13.128%   $189.5573   $189.56   $189.55   $189.60  
  Purchase #7 $236.87   12.724%   $267.0093   $267.01   $267.00   $267.00  
  7 purchase totals = $908.33       $1,010.9766   $1,010.98   $1,010.95   $1,011.00