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 $182.95   11.295%   $203.6142   $203.61   $203.60   $203.60  
  Purchase #2 $15.83   7.102%   $16.9542   $16.95   $16.95   $17.00  
  Purchase #3 $169.60   5.817%   $179.4656   $179.47   $179.45   $179.50  
  Purchase #4 $244.39   7.468%   $262.641   $262.64   $262.65   $262.60  
  Purchase #5 $25.99   11.572%   $28.9976   $29.00   $29.00   $29.00  
  Purchase #6 $6.28   10.438%   $6.9355   $6.94   $6.95   $6.90  
  Purchase #7 $99.80   6.686%   $106.4726   $106.47   $106.45   $106.50  
  7 purchase totals = $744.84       $805.0807   $805.08   $805.05   $805.10