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 $92.27   13.331%   $104.5705   $104.57   $104.55   $104.60  
  Purchase #2 $166.92   9.279%   $182.4085   $182.41   $182.40   $182.40  
  Purchase #3 $188.36   7.147%   $201.8221   $201.82   $201.80   $201.80  
  Purchase #4 $112.90   4.684%   $118.1882   $118.19   $118.20   $118.20  
  Purchase #5 $23.95   12.693%   $26.99   $26.99   $27.00   $27.00  
  Purchase #6 $233.79   3.436%   $241.823   $241.82   $241.80   $241.80  
  Purchase #7 $139.50   4.642%   $145.9756   $145.98   $146.00   $146.00  
  7 purchase totals = $957.69       $1,021.7779   $1,021.78   $1,021.75   $1,021.80