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 $53.69   3.401%   $55.516   $55.52   $55.50   $55.50  
  Purchase #2 $241.86   5.205%   $254.4488   $254.45   $254.45   $254.40  
  Purchase #3 $237.46   3.589%   $245.9824   $245.98   $246.00   $246.00  
  Purchase #4 $64.42   7.816%   $69.4551   $69.46   $69.45   $69.50  
  Purchase #5 $71.93   6.516%   $76.617   $76.62   $76.60   $76.60  
  Purchase #6 $64.45   13.699%   $73.279   $73.28   $73.30   $73.30  
  Purchase #7 $216.39   10.774%   $239.7039   $239.70   $239.70   $239.70  
  7 purchase totals = $950.20       $1,015.0022   $1,015.01   $1,015.00   $1,015.00