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 $201.33   12.610%   $226.7177   $226.72   $226.70   $226.70  
  Purchase #2 $250.96   9.637%   $275.145   $275.15   $275.15   $275.10  
  Purchase #3 $111.47   13.254%   $126.2442   $126.24   $126.25   $126.20  
  Purchase #4 $26.76   11.794%   $29.9161   $29.92   $29.90   $29.90  
  Purchase #5 $61.52   11.188%   $68.4029   $68.40   $68.40   $68.40  
  Purchase #6 $205.34   4.351%   $214.2743   $214.27   $214.25   $214.30  
  Purchase #7 $90.49   4.373%   $94.4471   $94.45   $94.45   $94.40  
  7 purchase totals = $947.87       $1,035.1473   $1,035.15   $1,035.10   $1,035.00