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 $16.43   3.638%   $17.0277   $17.03   $17.05   $17.00  
  Purchase #2 $240.42   5.688%   $254.0951   $254.10   $254.10   $254.10  
  Purchase #3 $79.37   6.751%   $84.7283   $84.73   $84.75   $84.70  
  Purchase #4 $143.86   8.156%   $155.5932   $155.59   $155.60   $155.60  
  Purchase #5 $239.84   4.515%   $250.6688   $250.67   $250.65   $250.70  
  Purchase #6 $23.92   10.396%   $26.4067   $26.41   $26.40   $26.40  
  Purchase #7 $230.96   6.800%   $246.6653   $246.67   $246.65   $246.70  
  7 purchase totals = $974.80       $1,035.1851   $1,035.20   $1,035.20   $1,035.20