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 $84.50   13.425%   $95.8441   $95.84   $95.85   $95.80  
  Purchase #2 $128.37   5.730%   $135.7256   $135.73   $135.75   $135.70  
  Purchase #3 $145.61   10.367%   $160.7054   $160.71   $160.70   $160.70  
  Purchase #4 $225.93   12.838%   $254.9349   $254.93   $254.95   $254.90  
  Purchase #5 $179.28   7.392%   $192.5324   $192.53   $192.55   $192.50  
  Purchase #6 $213.84   12.845%   $241.3077   $241.31   $241.30   $241.30  
  Purchase #7 $223.89   6.504%   $238.4518   $238.45   $238.45   $238.50  
  7 purchase totals = $1,201.42       $1,319.5019   $1,319.50   $1,319.55   $1,319.40