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 $76.27   10.197%   $84.0473   $84.05   $84.05   $84.00  
  Purchase #2 $164.57   8.678%   $178.8514   $178.85   $178.85   $178.90  
  Purchase #3 $199.61   12.137%   $223.8367   $223.84   $223.85   $223.80  
  Purchase #4 $161.49   6.415%   $171.8496   $171.85   $171.85   $171.80  
  Purchase #5 $151.33   12.484%   $170.222   $170.22   $170.20   $170.20  
  Purchase #6 $23.46   4.369%   $24.485   $24.49   $24.50   $24.50  
  Purchase #7 $145.99   4.158%   $152.0603   $152.06   $152.05   $152.10  
  7 purchase totals = $922.72       $1,005.3523   $1,005.36   $1,005.35   $1,005.30