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 $152.88   5.293%   $160.9719   $160.97   $160.95   $161.00  
  Purchase #2 $55.35   11.245%   $61.5741   $61.57   $61.55   $61.60  
  Purchase #3 $207.33   6.530%   $220.8686   $220.87   $220.85   $220.90  
  Purchase #4 $244.95   3.713%   $254.045   $254.05   $254.05   $254.00  
  Purchase #5 $48.63   9.617%   $53.3067   $53.31   $53.30   $53.30  
  Purchase #6 $117.65   13.498%   $133.5304   $133.53   $133.55   $133.50  
  Purchase #7 $84.45   4.104%   $87.9158   $87.92   $87.90   $87.90  
  7 purchase totals = $911.24       $972.2125   $972.22   $972.15   $972.20