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 $88.42   11.547%   $98.6299   $98.63   $98.65   $98.60  
  Purchase #2 $152.99   11.594%   $170.7277   $170.73   $170.75   $170.70  
  Purchase #3 $188.41   9.644%   $206.5803   $206.58   $206.60   $206.60  
  Purchase #4 $243.32   12.555%   $273.8688   $273.87   $273.85   $273.90  
  Purchase #5 $73.55   9.449%   $80.4997   $80.50   $80.50   $80.50  
  Purchase #6 $148.47   12.588%   $167.1594   $167.16   $167.15   $167.20  
  Purchase #7 $126.39   9.400%   $138.2707   $138.27   $138.25   $138.30  
  7 purchase totals = $1,021.55       $1,135.7365   $1,135.74   $1,135.75   $1,135.80