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 $9.81   3.690%   $10.172   $10.17   $10.15   $10.20  
  Purchase #2 $189.90   11.372%   $211.4954   $211.50   $211.50   $211.50  
  Purchase #3 $182.91   7.478%   $196.588   $196.59   $196.60   $196.60  
  Purchase #4 $244.75   11.485%   $272.8595   $272.86   $272.85   $272.90  
  Purchase #5 $163.94   9.367%   $179.2963   $179.30   $179.30   $179.30  
  Purchase #6 $110.51   6.257%   $117.4246   $117.42   $117.40   $117.40  
  Purchase #7 $193.41   8.703%   $210.2425   $210.24   $210.25   $210.20  
  7 purchase totals = $1,095.23       $1,198.0783   $1,198.08   $1,198.05   $1,198.10