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 $218.56   5.435%   $230.4387   $230.44   $230.45   $230.40  
  Purchase #2 $99.55   9.292%   $108.8002   $108.80   $108.80   $108.80  
  Purchase #3 $140.49   11.469%   $156.6028   $156.60   $156.60   $156.60  
  Purchase #4 $134.89   3.672%   $139.8432   $139.84   $139.85   $139.80  
  Purchase #5 $130.83   8.625%   $142.1141   $142.11   $142.10   $142.10  
  Purchase #6 $130.56   7.222%   $139.989   $139.99   $140.00   $140.00  
  Purchase #7 $165.66   4.448%   $173.0286   $173.03   $173.05   $173.00  
  7 purchase totals = $1,020.54       $1,090.8166   $1,090.81   $1,090.85   $1,090.70