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 $220.33   10.624%   $243.7379   $243.74   $243.75   $243.70  
  Purchase #2 $223.51   6.271%   $237.5263   $237.53   $237.55   $237.50  
  Purchase #3 $98.99   8.714%   $107.616   $107.62   $107.60   $107.60  
  Purchase #4 $233.89   7.372%   $251.1324   $251.13   $251.15   $251.10  
  Purchase #5 $67.96   4.278%   $70.8673   $70.87   $70.85   $70.90  
  Purchase #6 $92.82   10.733%   $102.7824   $102.78   $102.80   $102.80  
  Purchase #7 $54.76   12.485%   $61.5968   $61.60   $61.60   $61.60  
  7 purchase totals = $992.26       $1,075.2591   $1,075.27   $1,075.30   $1,075.20