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 $83.68   11.379%   $93.2019   $93.20   $93.20   $93.20  
  Purchase #2 $243.65   4.253%   $254.0124   $254.01   $254.00   $254.00  
  Purchase #3 $103.64   4.114%   $107.9037   $107.90   $107.90   $107.90  
  Purchase #4 $128.89   7.262%   $138.25   $138.25   $138.25   $138.30  
  Purchase #5 $22.47   8.547%   $24.3905   $24.39   $24.40   $24.40  
  Purchase #6 $95.57   11.432%   $106.4956   $106.50   $106.50   $106.50  
  Purchase #7 $235.88   4.678%   $246.9145   $246.91   $246.90   $246.90  
  7 purchase totals = $913.78       $971.1686   $971.16   $971.15   $971.20