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 $188.45   8.200%   $203.9029   $203.90   $203.90   $203.90  
  Purchase #2 $34.97   9.253%   $38.2058   $38.21   $38.20   $38.20  
  Purchase #3 $210.96   6.210%   $224.0606   $224.06   $224.05   $224.10  
  Purchase #4 $141.37   8.366%   $153.197   $153.20   $153.20   $153.20  
  Purchase #5 $80.66   11.432%   $89.8811   $89.88   $89.90   $89.90  
  Purchase #6 $184.75   8.422%   $200.3096   $200.31   $200.30   $200.30  
  Purchase #7 $207.49   8.520%   $225.1681   $225.17   $225.15   $225.20  
  7 purchase totals = $1,048.65       $1,134.7251   $1,134.73   $1,134.70   $1,134.80