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 $244.53   12.144%   $274.2257   $274.23   $274.25   $274.20  
  Purchase #2 $170.47   11.737%   $190.4781   $190.48   $190.50   $190.50  
  Purchase #3 $111.96   9.346%   $122.4238   $122.42   $122.40   $122.40  
  Purchase #4 $10.94   6.481%   $11.649   $11.65   $11.65   $11.60  
  Purchase #5 $71.44   6.351%   $75.9772   $75.98   $76.00   $76.00  
  Purchase #6 $138.84   8.780%   $151.0302   $151.03   $151.05   $151.00  
  Purchase #7 $191.92   7.676%   $206.6518   $206.65   $206.65   $206.70  
  7 purchase totals = $940.10       $1,032.4358   $1,032.44   $1,032.50   $1,032.40