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 $227.67   4.867%   $238.7507   $238.75   $238.75   $238.80  
  Purchase #2 $57.85   6.791%   $61.7786   $61.78   $61.80   $61.80  
  Purchase #3 $54.40   11.667%   $60.7468   $60.75   $60.75   $60.70  
  Purchase #4 $194.83   7.535%   $209.5104   $209.51   $209.50   $209.50  
  Purchase #5 $246.64   7.385%   $264.8544   $264.85   $264.85   $264.90  
  Purchase #6 $200.45   3.776%   $208.019   $208.02   $208.00   $208.00  
  Purchase #7 $53.50   10.134%   $58.9217   $58.92   $58.90   $58.90  
  7 purchase totals = $1,035.34       $1,102.5816   $1,102.58   $1,102.55   $1,102.60