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 $210.36   10.321%   $232.0713   $232.07   $232.05   $232.10  
  Purchase #2 $165.86   12.221%   $186.1298   $186.13   $186.15   $186.10  
  Purchase #3 $102.72   11.751%   $114.7906   $114.79   $114.80   $114.80  
  Purchase #4 $229.95   13.871%   $261.8464   $261.85   $261.85   $261.80  
  Purchase #5 $8.54   3.838%   $8.8678   $8.87   $8.85   $8.90  
  Purchase #6 $159.79   12.216%   $179.3099   $179.31   $179.30   $179.30  
  Purchase #7 $41.75   10.132%   $45.9801   $45.98   $46.00   $46.00  
  7 purchase totals = $918.97       $1,028.9959   $1,029.00   $1,029.00   $1,029.00