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 $41.87   12.106%   $46.9388   $46.94   $46.95   $46.90  
  Purchase #2 $184.47   4.432%   $192.6457   $192.65   $192.65   $192.60  
  Purchase #3 $137.64   9.869%   $151.2237   $151.22   $151.20   $151.20  
  Purchase #4 $72.82   11.670%   $81.3181   $81.32   $81.30   $81.30  
  Purchase #5 $120.89   13.212%   $136.862   $136.86   $136.85   $136.90  
  Purchase #6 $183.45   10.648%   $202.9838   $202.98   $203.00   $203.00  
  Purchase #7 $82.53   12.489%   $92.8372   $92.84   $92.85   $92.80  
  7 purchase totals = $823.67       $904.8093   $904.81   $904.80   $904.70