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 $52.93   6.765%   $56.5107   $56.51   $56.50   $56.50  
  Purchase #2 $52.30   5.867%   $55.3684   $55.37   $55.35   $55.40  
  Purchase #3 $148.86   13.872%   $169.5099   $169.51   $169.50   $169.50  
  Purchase #4 $221.45   6.555%   $235.966   $235.97   $235.95   $236.00  
  Purchase #5 $22.30   6.641%   $23.7809   $23.78   $23.80   $23.80  
  Purchase #6 $201.61   11.425%   $224.6439   $224.64   $224.65   $224.60  
  Purchase #7 $243.92   6.236%   $259.1309   $259.13   $259.15   $259.10  
  7 purchase totals = $943.37       $1,024.9107   $1,024.91   $1,024.90   $1,024.90