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 $181.59   6.254%   $192.9466   $192.95   $192.95   $192.90  
  Purchase #2 $244.39   6.790%   $260.9841   $260.98   $261.00   $261.00  
  Purchase #3 $82.68   4.515%   $86.413   $86.41   $86.40   $86.40  
  Purchase #4 $86.82   13.347%   $98.4079   $98.41   $98.40   $98.40  
  Purchase #5 $91.77   5.408%   $96.7329   $96.73   $96.75   $96.70  
  Purchase #6 $24.59   6.610%   $26.2154   $26.22   $26.20   $26.20  
  Purchase #7 $38.81   6.753%   $41.4308   $41.43   $41.45   $41.40  
  7 purchase totals = $750.65       $803.1307   $803.13   $803.15   $803.00