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 $95.92   10.159%   $105.6645   $105.66   $105.65   $105.70  
  Purchase #2 $139.45   6.191%   $148.0833   $148.08   $148.10   $148.10  
  Purchase #3 $80.87   10.864%   $89.6557   $89.66   $89.65   $89.70  
  Purchase #4 $106.62   12.744%   $120.2077   $120.21   $120.20   $120.20  
  Purchase #5 $50.80   9.268%   $55.5081   $55.51   $55.50   $55.50  
  Purchase #6 $185.95   3.119%   $191.7498   $191.75   $191.75   $191.70  
  Purchase #7 $186.60   6.837%   $199.3578   $199.36   $199.35   $199.40  
  7 purchase totals = $846.21       $910.2269   $910.23   $910.20   $910.30