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 $136.35   13.679%   $155.0013   $155.00   $155.00   $155.00  
  Purchase #2 $221.52   11.433%   $246.8464   $246.85   $246.85   $246.80  
  Purchase #3 $231.67   10.595%   $256.2154   $256.22   $256.20   $256.20  
  Purchase #4 $55.35   9.383%   $60.5435   $60.54   $60.55   $60.50  
  Purchase #5 $190.70   7.236%   $204.4991   $204.50   $204.50   $204.50  
  Purchase #6 $39.84   12.475%   $44.81   $44.81   $44.80   $44.80  
  Purchase #7 $77.55   11.280%   $86.2976   $86.30   $86.30   $86.30  
  7 purchase totals = $952.98       $1,054.2133   $1,054.22   $1,054.20   $1,054.10