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 $205.86   12.861%   $232.3357   $232.34   $232.35   $232.30  
  Purchase #2 $172.71   5.167%   $181.6339   $181.63   $181.65   $181.60  
  Purchase #3 $10.51   7.370%   $11.2846   $11.28   $11.30   $11.30  
  Purchase #4 $83.59   13.170%   $94.5988   $94.60   $94.60   $94.60  
  Purchase #5 $165.91   9.762%   $182.1061   $182.11   $182.10   $182.10  
  Purchase #6 $147.46   12.226%   $165.4885   $165.49   $165.50   $165.50  
  Purchase #7 $217.77   8.529%   $236.3436   $236.34   $236.35   $236.30  
  7 purchase totals = $1,003.81       $1,103.7912   $1,103.79   $1,103.85   $1,103.70