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 $91.51   13.818%   $104.1549   $104.15   $104.15   $104.20  
  Purchase #2 $138.79   6.357%   $147.6129   $147.61   $147.60   $147.60  
  Purchase #3 $239.68   12.208%   $268.9401   $268.94   $268.95   $268.90  
  Purchase #4 $249.70   6.344%   $265.541   $265.54   $265.55   $265.50  
  Purchase #5 $82.65   7.540%   $88.8818   $88.88   $88.90   $88.90  
  Purchase #6 $172.58   13.367%   $195.6488   $195.65   $195.65   $195.60  
  Purchase #7 $214.43   6.320%   $227.982   $227.98   $228.00   $228.00  
  7 purchase totals = $1,189.34       $1,298.7615   $1,298.75   $1,298.80   $1,298.70