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 $234.98   7.612%   $252.8667   $252.87   $252.85   $252.90  
  Purchase #2 $65.56   13.818%   $74.6191   $74.62   $74.60   $74.60  
  Purchase #3 $12.59   12.645%   $14.182   $14.18   $14.20   $14.20  
  Purchase #4 $183.48   13.516%   $208.2792   $208.28   $208.30   $208.30  
  Purchase #5 $59.86   9.700%   $65.6664   $65.67   $65.65   $65.70  
  Purchase #6 $101.33   10.835%   $112.3091   $112.31   $112.30   $112.30  
  Purchase #7 $16.27   6.370%   $17.3064   $17.31   $17.30   $17.30  
  7 purchase totals = $674.07       $745.2289   $745.24   $745.20   $745.30