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 $222.35   5.579%   $234.7549   $234.75   $234.75   $234.80  
  Purchase #2 $156.82   11.827%   $175.3671   $175.37   $175.35   $175.40  
  Purchase #3 $141.60   11.266%   $157.5527   $157.55   $157.55   $157.60  
  Purchase #4 $184.95   9.349%   $202.241   $202.24   $202.25   $202.20  
  Purchase #5 $25.47   10.140%   $28.0527   $28.05   $28.05   $28.10  
  Purchase #6 $206.42   12.861%   $232.9677   $232.97   $232.95   $233.00  
  Purchase #7 $56.76   7.341%   $60.9268   $60.93   $60.95   $60.90  
  7 purchase totals = $994.37       $1,091.8629   $1,091.86   $1,091.85   $1,092.00