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 $73.25   6.363%   $77.9109   $77.91   $77.90   $77.90  
  Purchase #2 $201.91   11.698%   $225.5294   $225.53   $225.55   $225.50  
  Purchase #3 $115.96   12.617%   $130.5907   $130.59   $130.60   $130.60  
  Purchase #4 $39.59   4.692%   $41.4476   $41.45   $41.45   $41.40  
  Purchase #5 $244.75   5.691%   $258.6787   $258.68   $258.70   $258.70  
  Purchase #6 $190.56   8.769%   $207.2702   $207.27   $207.25   $207.30  
  Purchase #7 $99.64   6.662%   $106.278   $106.28   $106.30   $106.30  
  7 purchase totals = $965.66       $1,047.7055   $1,047.71   $1,047.75   $1,047.70