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 $224.64   10.402%   $248.0071   $248.01   $248.00   $248.00  
  Purchase #2 $21.68   5.227%   $22.8132   $22.81   $22.80   $22.80  
  Purchase #3 $201.54   7.224%   $216.0992   $216.10   $216.10   $216.10  
  Purchase #4 $54.71   4.208%   $57.0122   $57.01   $57.00   $57.00  
  Purchase #5 $165.66   12.755%   $186.7899   $186.79   $186.80   $186.80  
  Purchase #6 $206.89   11.249%   $230.1631   $230.16   $230.15   $230.20  
  Purchase #7 $37.82   12.417%   $42.5161   $42.52   $42.50   $42.50  
  7 purchase totals = $912.94       $1,003.4008   $1,003.40   $1,003.35   $1,003.40