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 $77.25   12.174%   $86.6544   $86.65   $86.65   $86.70  
  Purchase #2 $249.83   8.674%   $271.5003   $271.50   $271.50   $271.50  
  Purchase #3 $72.36   6.681%   $77.1944   $77.19   $77.20   $77.20  
  Purchase #4 $247.80   11.589%   $276.5175   $276.52   $276.50   $276.50  
  Purchase #5 $53.95   7.586%   $58.0426   $58.04   $58.05   $58.00  
  Purchase #6 $115.38   6.427%   $122.7955   $122.80   $122.80   $122.80  
  Purchase #7 $248.80   11.570%   $277.5862   $277.59   $277.60   $277.60  
  7 purchase totals = $1,065.37       $1,170.2909   $1,170.29   $1,170.30   $1,170.30