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 $184.87   5.696%   $195.4002   $195.40   $195.40   $195.40  
  Purchase #2 $217.82   12.648%   $245.3699   $245.37   $245.35   $245.40  
  Purchase #3 $50.73   12.330%   $56.985   $56.99   $57.00   $57.00  
  Purchase #4 $58.78   13.209%   $66.5443   $66.54   $66.55   $66.50  
  Purchase #5 $121.61   11.162%   $135.1841   $135.18   $135.20   $135.20  
  Purchase #6 $120.57   6.815%   $128.7868   $128.79   $128.80   $128.80  
  Purchase #7 $190.38   7.379%   $204.4281   $204.43   $204.45   $204.40  
  7 purchase totals = $944.76       $1,032.6984   $1,032.70   $1,032.75   $1,032.70