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 $60.32   7.340%   $64.7475   $64.75   $64.75   $64.70  
  Purchase #2 $205.60   7.425%   $220.8658   $220.87   $220.85   $220.90  
  Purchase #3 $43.65   8.367%   $47.3022   $47.30   $47.30   $47.30  
  Purchase #4 $101.84   5.336%   $107.2742   $107.27   $107.25   $107.30  
  Purchase #5 $218.93   3.815%   $227.2822   $227.28   $227.30   $227.30  
  Purchase #6 $250.65   11.150%   $278.5975   $278.60   $278.60   $278.60  
  Purchase #7 $57.92   5.333%   $61.0089   $61.01   $61.00   $61.00  
  7 purchase totals = $938.91       $1,007.0783   $1,007.08   $1,007.05   $1,007.10