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 $244.99   7.647%   $263.7244   $263.72   $263.70   $263.70  
  Purchase #2 $189.76   7.836%   $204.6296   $204.63   $204.65   $204.60  
  Purchase #3 $41.66   3.348%   $43.0548   $43.05   $43.05   $43.10  
  Purchase #4 $203.84   4.298%   $212.601   $212.60   $212.60   $212.60  
  Purchase #5 $243.76   9.707%   $267.4218   $267.42   $267.40   $267.40  
  Purchase #6 $27.34   8.250%   $29.5956   $29.60   $29.60   $29.60  
  Purchase #7 $20.90   3.675%   $21.6681   $21.67   $21.65   $21.70  
  7 purchase totals = $972.25       $1,042.6953   $1,042.69   $1,042.65   $1,042.70