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 $162.76   8.251%   $176.1893   $176.19   $176.20   $176.20  
  Purchase #2 $6.41   12.376%   $7.2033   $7.20   $7.20   $7.20  
  Purchase #3 $161.54   9.747%   $177.2853   $177.29   $177.30   $177.30  
  Purchase #4 $196.82   12.627%   $221.6725   $221.67   $221.65   $221.70  
  Purchase #5 $133.82   13.804%   $152.2925   $152.29   $152.30   $152.30  
  Purchase #6 $186.49   3.380%   $192.7934   $192.79   $192.80   $192.80  
  Purchase #7 $90.76   9.201%   $99.1108   $99.11   $99.10   $99.10  
  7 purchase totals = $938.60       $1,026.5471   $1,026.54   $1,026.55   $1,026.60