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 $199.53   7.705%   $214.9038   $214.90   $214.90   $214.90  
  Purchase #2 $213.59   8.737%   $232.2514   $232.25   $232.25   $232.30  
  Purchase #3 $86.30   10.134%   $95.0456   $95.05   $95.05   $95.00  
  Purchase #4 $155.56   12.359%   $174.7857   $174.79   $174.80   $174.80  
  Purchase #5 $127.28   4.256%   $132.697   $132.70   $132.70   $132.70  
  Purchase #6 $59.26   9.578%   $64.9359   $64.94   $64.95   $64.90  
  Purchase #7 $29.56   13.505%   $33.5521   $33.55   $33.55   $33.60  
  7 purchase totals = $871.08       $948.1715   $948.18   $948.20   $948.20