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 $205.37   5.563%   $216.7947   $216.79   $216.80   $216.80  
  Purchase #2 $48.65   4.133%   $50.6607   $50.66   $50.65   $50.70  
  Purchase #3 $219.73   12.140%   $246.4052   $246.41   $246.40   $246.40  
  Purchase #4 $87.37   4.226%   $91.0623   $91.06   $91.05   $91.10  
  Purchase #5 $24.53   11.444%   $27.3372   $27.34   $27.35   $27.30  
  Purchase #6 $5.39   5.538%   $5.6885   $5.69   $5.70   $5.70  
  Purchase #7 $11.41   4.478%   $11.9209   $11.92   $11.90   $11.90  
  7 purchase totals = $602.45       $649.8695   $649.87   $649.85   $649.90