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 $41.64   7.267%   $44.666   $44.67   $44.65   $44.70  
  Purchase #2 $138.27   9.516%   $151.4278   $151.43   $151.45   $151.40  
  Purchase #3 $78.88   13.868%   $89.8191   $89.82   $89.80   $89.80  
  Purchase #4 $236.66   9.773%   $259.7888   $259.79   $259.80   $259.80  
  Purchase #5 $213.49   13.454%   $242.2129   $242.21   $242.20   $242.20  
  Purchase #6 $49.25   11.844%   $55.0832   $55.08   $55.10   $55.10  
  Purchase #7 $159.37   13.608%   $181.0571   $181.06   $181.05   $181.10  
  7 purchase totals = $917.56       $1,024.0549   $1,024.06   $1,024.05   $1,024.10