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 $236.48   5.658%   $249.86   $249.86   $249.85   $249.90  
  Purchase #2 $71.52   5.488%   $75.445   $75.45   $75.45   $75.40  
  Purchase #3 $146.69   6.191%   $155.7716   $155.77   $155.75   $155.80  
  Purchase #4 $246.88   12.838%   $278.5745   $278.57   $278.55   $278.60  
  Purchase #5 $95.79   6.473%   $101.9905   $101.99   $102.00   $102.00  
  Purchase #6 $75.70   5.694%   $80.0104   $80.01   $80.00   $80.00  
  Purchase #7 $231.80   13.687%   $263.5265   $263.53   $263.55   $263.50  
  7 purchase totals = $1,104.86       $1,205.1785   $1,205.18   $1,205.15   $1,205.20