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 $213.56   6.581%   $227.6144   $227.61   $227.60   $227.60  
  Purchase #2 $167.65   5.117%   $176.2287   $176.23   $176.25   $176.20  
  Purchase #3 $190.48   5.345%   $200.6612   $200.66   $200.65   $200.70  
  Purchase #4 $246.75   8.816%   $268.5035   $268.50   $268.50   $268.50  
  Purchase #5 $218.88   5.268%   $230.4106   $230.41   $230.40   $230.40  
  Purchase #6 $108.31   6.228%   $115.0555   $115.06   $115.05   $115.10  
  Purchase #7 $247.93   8.263%   $268.4165   $268.42   $268.40   $268.40  
  7 purchase totals = $1,393.56       $1,486.8904   $1,486.89   $1,486.85   $1,486.90