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 $103.68   6.775%   $110.7043   $110.70   $110.70   $110.70  
  Purchase #2 $6.36   7.184%   $6.8169   $6.82   $6.80   $6.80  
  Purchase #3 $227.94   8.326%   $246.9183   $246.92   $246.90   $246.90  
  Purchase #4 $153.53   3.458%   $158.8391   $158.84   $158.85   $158.80  
  Purchase #5 $186.88   8.517%   $202.7966   $202.80   $202.80   $202.80  
  Purchase #6 $203.44   6.364%   $216.3869   $216.39   $216.40   $216.40  
  Purchase #7 $91.68   9.544%   $100.4299   $100.43   $100.45   $100.40  
  7 purchase totals = $973.51       $1,042.8920   $1,042.90   $1,042.90   $1,042.80