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 $57.93   6.593%   $61.7493   $61.75   $61.75   $61.70  
  Purchase #2 $61.85   6.286%   $65.7379   $65.74   $65.75   $65.70  
  Purchase #3 $183.49   8.855%   $199.738   $199.74   $199.75   $199.70  
  Purchase #4 $195.66   6.864%   $209.0901   $209.09   $209.10   $209.10  
  Purchase #5 $97.80   10.331%   $107.9037   $107.90   $107.90   $107.90  
  Purchase #6 $226.73   12.203%   $254.3979   $254.40   $254.40   $254.40  
  Purchase #7 $121.73   12.190%   $136.5689   $136.57   $136.55   $136.60  
  7 purchase totals = $945.19       $1,035.1858   $1,035.19   $1,035.20   $1,035.10