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 $246.63   8.714%   $268.1213   $268.12   $268.10   $268.10  
  Purchase #2 $160.63   7.483%   $172.6499   $172.65   $172.65   $172.60  
  Purchase #3 $64.99   11.497%   $72.4619   $72.46   $72.45   $72.50  
  Purchase #4 $87.43   8.281%   $94.6701   $94.67   $94.65   $94.70  
  Purchase #5 $7.87   3.142%   $8.1173   $8.12   $8.10   $8.10  
  Purchase #6 $170.81   10.320%   $188.4376   $188.44   $188.45   $188.40  
  Purchase #7 $199.74   11.665%   $223.0397   $223.04   $223.05   $223.00  
  7 purchase totals = $938.10       $1,027.4978   $1,027.50   $1,027.45   $1,027.40