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 $63.89   8.137%   $69.0887   $69.09   $69.10   $69.10  
  Purchase #2 $168.98   7.793%   $182.1486   $182.15   $182.15   $182.10  
  Purchase #3 $68.83   3.297%   $71.0993   $71.10   $71.10   $71.10  
  Purchase #4 $20.38   12.581%   $22.944   $22.94   $22.95   $22.90  
  Purchase #5 $241.91   3.390%   $250.1107   $250.11   $250.10   $250.10  
  Purchase #6 $203.61   12.544%   $229.1508   $229.15   $229.15   $229.20  
  Purchase #7 $201.49   6.618%   $214.8246   $214.82   $214.80   $214.80  
  7 purchase totals = $969.09       $1,039.3667   $1,039.36   $1,039.35   $1,039.30