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 $87.46   12.625%   $98.5018   $98.50   $98.50   $98.50  
  Purchase #2 $31.88   13.629%   $36.2249   $36.22   $36.20   $36.20  
  Purchase #3 $57.74   13.251%   $65.3911   $65.39   $65.40   $65.40  
  Purchase #4 $163.84   10.587%   $181.1857   $181.19   $181.20   $181.20  
  Purchase #5 $244.96   8.728%   $266.3401   $266.34   $266.35   $266.30  
  Purchase #6 $178.91   8.795%   $194.6451   $194.65   $194.65   $194.60  
  Purchase #7 $162.51   10.584%   $179.7101   $179.71   $179.70   $179.70  
  7 purchase totals = $927.30       $1,021.9988   $1,022.00   $1,022.00   $1,021.90