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 $237.38   11.575%   $264.8567   $264.86   $264.85   $264.90  
  Purchase #2 $38.56   6.273%   $40.9789   $40.98   $41.00   $41.00  
  Purchase #3 $243.47   4.707%   $254.9301   $254.93   $254.95   $254.90  
  Purchase #4 $155.65   10.386%   $171.8158   $171.82   $171.80   $171.80  
  Purchase #5 $168.89   9.862%   $185.5459   $185.55   $185.55   $185.50  
  Purchase #6 $28.26   8.273%   $30.5979   $30.60   $30.60   $30.60  
  Purchase #7 $232.26   9.179%   $253.5791   $253.58   $253.60   $253.60  
  7 purchase totals = $1,104.47       $1,202.3044   $1,202.32   $1,202.35   $1,202.30