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 $197.79   8.469%   $214.5408   $214.54   $214.55   $214.50  
  Purchase #2 $211.39   11.793%   $236.3192   $236.32   $236.30   $236.30  
  Purchase #3 $97.28   10.733%   $107.7211   $107.72   $107.70   $107.70  
  Purchase #4 $214.83   6.857%   $229.5609   $229.56   $229.55   $229.60  
  Purchase #5 $54.46   7.578%   $58.587   $58.59   $58.60   $58.60  
  Purchase #6 $98.92   7.445%   $106.2846   $106.28   $106.30   $106.30  
  Purchase #7 $43.27   9.452%   $47.3599   $47.36   $47.35   $47.40  
  7 purchase totals = $917.94       $1,000.3735   $1,000.37   $1,000.35   $1,000.40