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 $56.35   8.763%   $61.288   $61.29   $61.30   $61.30  
  Purchase #2 $199.64   4.179%   $207.983   $207.98   $208.00   $208.00  
  Purchase #3 $51.65   11.152%   $57.41   $57.41   $57.40   $57.40  
  Purchase #4 $159.77   8.364%   $173.1332   $173.13   $173.15   $173.10  
  Purchase #5 $221.61   5.321%   $233.4019   $233.40   $233.40   $233.40  
  Purchase #6 $170.76   6.422%   $181.7262   $181.73   $181.75   $181.70  
  Purchase #7 $79.60   5.483%   $83.9645   $83.96   $83.95   $84.00  
  7 purchase totals = $939.38       $998.9068   $998.90   $998.95   $998.90