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 $39.56   12.511%   $44.5094   $44.51   $44.50   $44.50  
  Purchase #2 $73.88   13.280%   $83.6913   $83.69   $83.70   $83.70  
  Purchase #3 $131.35   9.297%   $143.5616   $143.56   $143.55   $143.60  
  Purchase #4 $193.55   3.258%   $199.8559   $199.86   $199.85   $199.90  
  Purchase #5 $181.85   10.284%   $200.5515   $200.55   $200.55   $200.60  
  Purchase #6 $65.83   11.213%   $73.2115   $73.21   $73.20   $73.20  
  Purchase #7 $203.87   6.435%   $216.989   $216.99   $217.00   $217.00  
  7 purchase totals = $889.89       $962.3702   $962.37   $962.35   $962.50