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 $176.98   11.599%   $197.5079   $197.51   $197.50   $197.50  
  Purchase #2 $214.37   9.518%   $234.7737   $234.77   $234.75   $234.80  
  Purchase #3 $24.67   9.464%   $27.0048   $27.00   $27.00   $27.00  
  Purchase #4 $71.32   11.817%   $79.7479   $79.75   $79.75   $79.70  
  Purchase #5 $168.49   5.284%   $177.393   $177.39   $177.40   $177.40  
  Purchase #6 $56.42   9.392%   $61.719   $61.72   $61.70   $61.70  
  Purchase #7 $26.33   6.644%   $28.0794   $28.08   $28.10   $28.10  
  7 purchase totals = $738.58       $806.2257   $806.22   $806.20   $806.20