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 $86.76   5.275%   $91.3366   $91.34   $91.35   $91.30  
  Purchase #2 $138.51   5.587%   $146.2486   $146.25   $146.25   $146.20  
  Purchase #3 $194.54   10.151%   $214.2878   $214.29   $214.30   $214.30  
  Purchase #4 $203.72   11.690%   $227.5349   $227.53   $227.55   $227.50  
  Purchase #5 $118.46   12.761%   $133.5767   $133.58   $133.60   $133.60  
  Purchase #6 $196.62   8.168%   $212.6799   $212.68   $212.70   $212.70  
  Purchase #7 $17.60   10.453%   $19.4397   $19.44   $19.45   $19.40  
  7 purchase totals = $956.21       $1,045.1042   $1,045.11   $1,045.20   $1,045.00