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 $19.45   7.383%   $20.886   $20.89   $20.90   $20.90  
  Purchase #2 $160.65   13.156%   $181.7851   $181.79   $181.80   $181.80  
  Purchase #3 $188.57   7.425%   $202.5713   $202.57   $202.55   $202.60  
  Purchase #4 $231.47   3.426%   $239.4002   $239.40   $239.40   $239.40  
  Purchase #5 $137.37   11.220%   $152.7829   $152.78   $152.80   $152.80  
  Purchase #6 $195.64   10.440%   $216.0648   $216.06   $216.05   $216.10  
  Purchase #7 $95.83   6.553%   $102.1097   $102.11   $102.10   $102.10  
  7 purchase totals = $1,028.98       $1,115.6000   $1,115.60   $1,115.60   $1,115.70