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 $242.46   13.840%   $276.0165   $276.02   $276.00   $276.00  
  Purchase #2 $32.67   6.527%   $34.8024   $34.80   $34.80   $34.80  
  Purchase #3 $218.55   12.731%   $246.3736   $246.37   $246.35   $246.40  
  Purchase #4 $55.55   11.330%   $61.8438   $61.84   $61.85   $61.80  
  Purchase #5 $84.68   3.121%   $87.3229   $87.32   $87.30   $87.30  
  Purchase #6 $145.64   7.775%   $156.9635   $156.96   $156.95   $157.00  
  Purchase #7 $233.77   11.516%   $260.691   $260.69   $260.70   $260.70  
  7 purchase totals = $1,013.32       $1,124.0137   $1,124.00   $1,123.95   $1,124.00