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 $207.61   13.639%   $235.9259   $235.93   $235.95   $235.90  
  Purchase #2 $223.94   7.851%   $241.5215   $241.52   $241.50   $241.50  
  Purchase #3 $91.94   5.695%   $97.176   $97.18   $97.20   $97.20  
  Purchase #4 $18.40   9.751%   $20.1942   $20.19   $20.20   $20.20  
  Purchase #5 $145.85   5.427%   $153.7653   $153.77   $153.75   $153.80  
  Purchase #6 $230.78   6.591%   $245.9907   $245.99   $246.00   $246.00  
  Purchase #7 $246.85   6.367%   $262.5669   $262.57   $262.55   $262.60  
  7 purchase totals = $1,165.37       $1,257.1405   $1,257.15   $1,257.15   $1,257.20