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 $49.36   8.348%   $53.4806   $53.48   $53.50   $53.50  
  Purchase #2 $188.26   3.779%   $195.3743   $195.37   $195.35   $195.40  
  Purchase #3 $220.59   5.317%   $232.3188   $232.32   $232.30   $232.30  
  Purchase #4 $166.78   10.296%   $183.9517   $183.95   $183.95   $184.00  
  Purchase #5 $127.26   6.618%   $135.6821   $135.68   $135.70   $135.70  
  Purchase #6 $121.68   6.561%   $129.6634   $129.66   $129.65   $129.70  
  Purchase #7 $120.26   8.823%   $130.8705   $130.87   $130.85   $130.90  
  7 purchase totals = $994.19       $1,061.3414   $1,061.33   $1,061.30   $1,061.50