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 $249.86   10.798%   $276.8399   $276.84   $276.85   $276.80  
  Purchase #2 $232.59   5.486%   $245.3499   $245.35   $245.35   $245.30  
  Purchase #3 $98.33   10.700%   $108.8513   $108.85   $108.85   $108.90  
  Purchase #4 $144.55   4.438%   $150.9651   $150.97   $150.95   $151.00  
  Purchase #5 $244.56   8.295%   $264.8463   $264.85   $264.85   $264.80  
  Purchase #6 $213.31   6.757%   $227.7234   $227.72   $227.70   $227.70  
  Purchase #7 $92.96   3.540%   $96.2508   $96.25   $96.25   $96.30  
  7 purchase totals = $1,276.16       $1,370.8267   $1,370.83   $1,370.80   $1,370.80