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 $76.41   3.126%   $78.7986   $78.80   $78.80   $78.80  
  Purchase #2 $191.51   9.131%   $208.9968   $209.00   $209.00   $209.00  
  Purchase #3 $130.87   3.231%   $135.0984   $135.10   $135.10   $135.10  
  Purchase #4 $193.65   5.485%   $204.2717   $204.27   $204.25   $204.30  
  Purchase #5 $16.76   4.756%   $17.5571   $17.56   $17.55   $17.60  
  Purchase #6 $124.25   4.169%   $129.43   $129.43   $129.45   $129.40  
  Purchase #7 $226.64   7.574%   $243.8057   $243.81   $243.80   $243.80  
  7 purchase totals = $960.09       $1,017.9583   $1,017.97   $1,017.95   $1,018.00