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 $61.96   9.796%   $68.0296   $68.03   $68.05   $68.00  
  Purchase #2 $250.82   12.554%   $282.3079   $282.31   $282.30   $282.30  
  Purchase #3 $192.98   8.696%   $209.7615   $209.76   $209.75   $209.80  
  Purchase #4 $126.83   6.121%   $134.5933   $134.59   $134.60   $134.60  
  Purchase #5 $64.84   7.574%   $69.751   $69.75   $69.75   $69.80  
  Purchase #6 $153.70   11.688%   $171.6645   $171.66   $171.65   $171.70  
  Purchase #7 $84.72   7.414%   $91.0011   $91.00   $91.00   $91.00  
  7 purchase totals = $935.85       $1,027.1089   $1,027.10   $1,027.10   $1,027.20