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 $152.54   10.689%   $168.845   $168.85   $168.85   $168.80  
  Purchase #2 $12.69   5.127%   $13.3406   $13.34   $13.35   $13.30  
  Purchase #3 $48.43   4.405%   $50.5633   $50.56   $50.55   $50.60  
  Purchase #4 $192.59   5.514%   $203.2094   $203.21   $203.20   $203.20  
  Purchase #5 $36.91   5.657%   $38.998   $39.00   $39.00   $39.00  
  Purchase #6 $144.44   9.517%   $158.1864   $158.19   $158.20   $158.20  
  Purchase #7 $148.65   4.171%   $154.8502   $154.85   $154.85   $154.90  
  7 purchase totals = $736.25       $787.9929   $788.00   $788.00   $788.00