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 $191.86   5.254%   $201.9403   $201.94   $201.95   $201.90  
  Purchase #2 $19.39   6.117%   $20.5761   $20.58   $20.60   $20.60  
  Purchase #3 $127.75   11.221%   $142.0848   $142.08   $142.10   $142.10  
  Purchase #4 $90.32   5.757%   $95.5197   $95.52   $95.50   $95.50  
  Purchase #5 $167.52   4.406%   $174.9009   $174.90   $174.90   $174.90  
  Purchase #6 $115.83   11.557%   $129.2165   $129.22   $129.20   $129.20  
  Purchase #7 $176.81   9.480%   $193.5716   $193.57   $193.55   $193.60  
  7 purchase totals = $889.48       $957.8099   $957.81   $957.80   $957.80