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 $67.60   8.686%   $73.4717   $73.47   $73.45   $73.50  
  Purchase #2 $92.52   10.826%   $102.5362   $102.54   $102.55   $102.50  
  Purchase #3 $107.68   3.686%   $111.6491   $111.65   $111.65   $111.60  
  Purchase #4 $222.32   12.483%   $250.0722   $250.07   $250.05   $250.10  
  Purchase #5 $182.67   11.146%   $203.0304   $203.03   $203.05   $203.00  
  Purchase #6 $163.99   9.711%   $179.9151   $179.92   $179.90   $179.90  
  Purchase #7 $85.70   9.355%   $93.7172   $93.72   $93.70   $93.70  
  7 purchase totals = $922.48       $1,014.3919   $1,014.40   $1,014.35   $1,014.30