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 $61.29   7.807%   $66.0749   $66.07   $66.05   $66.10  
  Purchase #2 $219.76   12.763%   $247.808   $247.81   $247.80   $247.80  
  Purchase #3 $238.33   6.834%   $254.6175   $254.62   $254.60   $254.60  
  Purchase #4 $203.91   3.829%   $211.7177   $211.72   $211.70   $211.70  
  Purchase #5 $186.75   8.429%   $202.4912   $202.49   $202.50   $202.50  
  Purchase #6 $26.44   4.502%   $27.6303   $27.63   $27.65   $27.60  
  Purchase #7 $46.48   6.788%   $49.6351   $49.64   $49.65   $49.60  
  7 purchase totals = $982.96       $1,059.9747   $1,059.98   $1,059.95   $1,059.90