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 $43.56   8.672%   $47.3375   $47.34   $47.35   $47.30  
  Purchase #2 $110.84   7.172%   $118.7894   $118.79   $118.80   $118.80  
  Purchase #3 $243.32   11.421%   $271.1096   $271.11   $271.10   $271.10  
  Purchase #4 $53.91   11.714%   $60.225   $60.23   $60.25   $60.20  
  Purchase #5 $92.84   6.369%   $98.753   $98.75   $98.75   $98.80  
  Purchase #6 $224.86   6.218%   $238.8418   $238.84   $238.85   $238.80  
  Purchase #7 $164.40   3.518%   $170.1836   $170.18   $170.20   $170.20  
  7 purchase totals = $933.73       $1,005.2399   $1,005.24   $1,005.30   $1,005.20