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 $54.92   3.690%   $56.9465   $56.95   $56.95   $56.90  
  Purchase #2 $124.35   7.110%   $133.1913   $133.19   $133.20   $133.20  
  Purchase #3 $17.50   7.315%   $18.7801   $18.78   $18.80   $18.80  
  Purchase #4 $181.54   3.387%   $187.6888   $187.69   $187.70   $187.70  
  Purchase #5 $14.70   13.369%   $16.6652   $16.67   $16.65   $16.70  
  Purchase #6 $125.35   7.229%   $134.4116   $134.41   $134.40   $134.40  
  Purchase #7 $80.61   3.229%   $83.2129   $83.21   $83.20   $83.20  
  7 purchase totals = $598.97       $630.8964   $630.90   $630.90   $630.90