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 $168.73   8.350%   $182.819   $182.82   $182.80   $182.80  
  Purchase #2 $160.68   13.118%   $181.758   $181.76   $181.75   $181.80  
  Purchase #3 $94.34   13.453%   $107.0316   $107.03   $107.05   $107.00  
  Purchase #4 $143.88   13.227%   $162.911   $162.91   $162.90   $162.90  
  Purchase #5 $227.90   7.752%   $245.5668   $245.57   $245.55   $245.60  
  Purchase #6 $243.25   8.768%   $264.5782   $264.58   $264.60   $264.60  
  Purchase #7 $96.70   8.316%   $104.7416   $104.74   $104.75   $104.70  
  7 purchase totals = $1,135.48       $1,249.4062   $1,249.41   $1,249.40   $1,249.40