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 $58.33   6.629%   $62.1967   $62.20   $62.20   $62.20  
  Purchase #2 $238.62   8.777%   $259.5637   $259.56   $259.55   $259.60  
  Purchase #3 $120.67   13.318%   $136.7408   $136.74   $136.75   $136.70  
  Purchase #4 $86.85   3.232%   $89.657   $89.66   $89.65   $89.70  
  Purchase #5 $54.61   5.415%   $57.5671   $57.57   $57.55   $57.60  
  Purchase #6 $7.67   11.855%   $8.5793   $8.58   $8.60   $8.60  
  Purchase #7 $180.43   4.146%   $187.9106   $187.91   $187.90   $187.90  
  7 purchase totals = $747.18       $802.2152   $802.22   $802.20   $802.30