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 $248.96   10.154%   $274.2394   $274.24   $274.25   $274.20  
  Purchase #2 $21.25   9.584%   $23.2866   $23.29   $23.30   $23.30  
  Purchase #3 $238.70   12.700%   $269.0149   $269.01   $269.00   $269.00  
  Purchase #4 $163.87   9.313%   $179.1312   $179.13   $179.15   $179.10  
  Purchase #5 $54.73   13.197%   $61.9527   $61.95   $61.95   $62.00  
  Purchase #6 $238.47   13.752%   $271.2644   $271.26   $271.25   $271.30  
  Purchase #7 $152.94   8.153%   $165.4092   $165.41   $165.40   $165.40  
  7 purchase totals = $1,118.92       $1,244.2984   $1,244.29   $1,244.30   $1,244.30