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 $239.61   10.695%   $265.2363   $265.24   $265.25   $265.20  
  Purchase #2 $185.56   5.614%   $195.9773   $195.98   $196.00   $196.00  
  Purchase #3 $29.35   11.655%   $32.7707   $32.77   $32.75   $32.80  
  Purchase #4 $200.42   9.592%   $219.6443   $219.64   $219.65   $219.60  
  Purchase #5 $223.79   6.393%   $238.0969   $238.10   $238.10   $238.10  
  Purchase #6 $80.98   12.290%   $90.9324   $90.93   $90.95   $90.90  
  Purchase #7 $214.53   8.459%   $232.6771   $232.68   $232.70   $232.70  
  7 purchase totals = $1,174.24       $1,275.3350   $1,275.34   $1,275.40   $1,275.30