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 $234.36   8.482%   $254.2384   $254.24   $254.25   $254.20  
  Purchase #2 $150.29   9.398%   $164.4143   $164.41   $164.40   $164.40  
  Purchase #3 $34.72   12.232%   $38.967   $38.97   $38.95   $39.00  
  Purchase #4 $30.48   8.669%   $33.1223   $33.12   $33.10   $33.10  
  Purchase #5 $104.90   10.591%   $116.01   $116.01   $116.00   $116.00  
  Purchase #6 $225.44   9.864%   $247.6774   $247.68   $247.70   $247.70  
  Purchase #7 $21.45   10.210%   $23.64   $23.64   $23.65   $23.60  
  7 purchase totals = $801.64       $878.0694   $878.07   $878.05   $878.00