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 $205.68   7.215%   $220.5198   $220.52   $220.50   $220.50  
  Purchase #2 $149.67   4.784%   $156.8302   $156.83   $156.85   $156.80  
  Purchase #3 $69.66   6.442%   $74.1475   $74.15   $74.15   $74.10  
  Purchase #4 $249.83   6.729%   $266.6411   $266.64   $266.65   $266.60  
  Purchase #5 $77.37   12.112%   $86.7411   $86.74   $86.75   $86.70  
  Purchase #6 $174.90   3.837%   $181.6109   $181.61   $181.60   $181.60  
  Purchase #7 $194.35   6.195%   $206.39   $206.39   $206.40   $206.40  
  7 purchase totals = $1,121.46       $1,192.8806   $1,192.88   $1,192.90   $1,192.70