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 $181.32   6.532%   $193.1638   $193.16   $193.15   $193.20  
  Purchase #2 $94.46   10.662%   $104.5313   $104.53   $104.55   $104.50  
  Purchase #3 $14.58   12.706%   $16.4325   $16.43   $16.45   $16.40  
  Purchase #4 $75.82   13.386%   $85.9693   $85.97   $85.95   $86.00  
  Purchase #5 $153.97   9.525%   $168.6356   $168.64   $168.65   $168.60  
  Purchase #6 $142.66   6.435%   $151.8402   $151.84   $151.85   $151.80  
  Purchase #7 $80.75   6.670%   $86.136   $86.14   $86.15   $86.10  
  7 purchase totals = $743.56       $806.7087   $806.71   $806.75   $806.60