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 $227.73   3.183%   $234.9786   $234.98   $235.00   $235.00  
  Purchase #2 $163.42   11.308%   $181.8995   $181.90   $181.90   $181.90  
  Purchase #3 $6.25   11.655%   $6.9784   $6.98   $7.00   $7.00  
  Purchase #4 $199.50   12.278%   $223.9946   $223.99   $224.00   $224.00  
  Purchase #5 $117.88   11.436%   $131.3608   $131.36   $131.35   $131.40  
  Purchase #6 $94.95   7.392%   $101.9687   $101.97   $101.95   $102.00  
  Purchase #7 $127.32   11.213%   $141.5964   $141.60   $141.60   $141.60  
  7 purchase totals = $937.05       $1,022.7770   $1,022.78   $1,022.80   $1,022.90