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 $77.51   8.610%   $84.1836   $84.18   $84.20   $84.20  
  Purchase #2 $239.36   11.282%   $266.3646   $266.36   $266.35   $266.40  
  Purchase #3 $152.78   10.288%   $168.498   $168.50   $168.50   $168.50  
  Purchase #4 $122.34   12.395%   $137.504   $137.50   $137.50   $137.50  
  Purchase #5 $180.80   11.629%   $201.8252   $201.83   $201.85   $201.80  
  Purchase #6 $245.86   8.789%   $267.4686   $267.47   $267.45   $267.50  
  Purchase #7 $217.52   12.700%   $245.145   $245.15   $245.15   $245.10  
  7 purchase totals = $1,236.17       $1,370.9890   $1,370.99   $1,371.00   $1,371.00