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 $183.28   6.451%   $195.1034   $195.10   $195.10   $195.10  
  Purchase #2 $54.57   3.211%   $56.3222   $56.32   $56.30   $56.30  
  Purchase #3 $72.97   10.430%   $80.5808   $80.58   $80.60   $80.60  
  Purchase #4 $55.58   6.548%   $59.2194   $59.22   $59.20   $59.20  
  Purchase #5 $30.95   11.754%   $34.5879   $34.59   $34.60   $34.60  
  Purchase #6 $73.55   13.203%   $83.2608   $83.26   $83.25   $83.30  
  Purchase #7 $235.99   8.136%   $255.1901   $255.19   $255.20   $255.20  
  7 purchase totals = $706.89       $764.2646   $764.26   $764.25   $764.30