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 $93.30   5.855%   $98.7627   $98.76   $98.75   $98.80  
  Purchase #2 $189.62   3.537%   $196.3269   $196.33   $196.35   $196.30  
  Purchase #3 $240.47   4.369%   $250.9761   $250.98   $251.00   $251.00  
  Purchase #4 $171.84   5.283%   $180.9183   $180.92   $180.90   $180.90  
  Purchase #5 $247.69   12.582%   $278.8544   $278.85   $278.85   $278.90  
  Purchase #6 $26.96   10.584%   $29.8134   $29.81   $29.80   $29.80  
  Purchase #7 $230.94   4.118%   $240.4501   $240.45   $240.45   $240.50  
  7 purchase totals = $1,200.82       $1,276.1019   $1,276.10   $1,276.10   $1,276.20