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 $53.99   11.182%   $60.0272   $60.03   $60.05   $60.00  
  Purchase #2 $155.31   11.157%   $172.6379   $172.64   $172.65   $172.60  
  Purchase #3 $220.40   5.560%   $232.6542   $232.65   $232.65   $232.70  
  Purchase #4 $183.62   10.577%   $203.0415   $203.04   $203.05   $203.00  
  Purchase #5 $212.40   10.709%   $235.1459   $235.15   $235.15   $235.10  
  Purchase #6 $97.76   12.339%   $109.8226   $109.82   $109.80   $109.80  
  Purchase #7 $8.80   10.517%   $9.7255   $9.73   $9.75   $9.70  
  7 purchase totals = $932.28       $1,023.0548   $1,023.06   $1,023.10   $1,022.90