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 $46.44   13.165%   $52.5538   $52.55   $52.55   $52.60  
  Purchase #2 $160.61   7.629%   $172.8629   $172.86   $172.85   $172.90  
  Purchase #3 $228.88   5.477%   $241.4158   $241.42   $241.40   $241.40  
  Purchase #4 $129.45   4.723%   $135.5639   $135.56   $135.55   $135.60  
  Purchase #5 $250.28   7.343%   $268.6581   $268.66   $268.65   $268.70  
  Purchase #6 $58.63   6.669%   $62.54   $62.54   $62.55   $62.50  
  Purchase #7 $205.30   12.350%   $230.6546   $230.65   $230.65   $230.70  
  7 purchase totals = $1,079.59       $1,164.2491   $1,164.24   $1,164.20   $1,164.40