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 $244.37   8.746%   $265.7426   $265.74   $265.75   $265.70  
  Purchase #2 $243.31   6.462%   $259.0327   $259.03   $259.05   $259.00  
  Purchase #3 $37.29   13.694%   $42.3965   $42.40   $42.40   $42.40  
  Purchase #4 $82.55   5.483%   $87.0762   $87.08   $87.10   $87.10  
  Purchase #5 $231.39   4.832%   $242.5708   $242.57   $242.55   $242.60  
  Purchase #6 $245.78   5.180%   $258.5114   $258.51   $258.50   $258.50  
  Purchase #7 $10.27   4.299%   $10.7115   $10.71   $10.70   $10.70  
  7 purchase totals = $1,094.96       $1,166.0417   $1,166.04   $1,166.05   $1,166.00