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 $238.78   11.217%   $265.564   $265.56   $265.55   $265.60  
  Purchase #2 $240.89   12.661%   $271.3891   $271.39   $271.40   $271.40  
  Purchase #3 $182.85   7.631%   $196.8033   $196.80   $196.80   $196.80  
  Purchase #4 $234.57   12.557%   $264.025   $264.03   $264.05   $264.00  
  Purchase #5 $226.80   11.491%   $252.8616   $252.86   $252.85   $252.90  
  Purchase #6 $95.79   4.373%   $99.9789   $99.98   $100.00   $100.00  
  Purchase #7 $219.48   12.407%   $246.7109   $246.71   $246.70   $246.70  
  7 purchase totals = $1,439.16       $1,597.3328   $1,597.33   $1,597.35   $1,597.40