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 $236.94   10.864%   $262.6812   $262.68   $262.70   $262.70  
  Purchase #2 $117.48   13.194%   $132.9803   $132.98   $133.00   $133.00  
  Purchase #3 $239.33   7.436%   $257.1266   $257.13   $257.15   $257.10  
  Purchase #4 $71.90   7.714%   $77.4464   $77.45   $77.45   $77.40  
  Purchase #5 $226.34   10.194%   $249.4131   $249.41   $249.40   $249.40  
  Purchase #6 $198.73   6.605%   $211.8561   $211.86   $211.85   $211.90  
  Purchase #7 $35.98   4.480%   $37.5919   $37.59   $37.60   $37.60  
  7 purchase totals = $1,126.70       $1,229.0956   $1,229.10   $1,229.15   $1,229.10