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 $178.85   11.628%   $199.6467   $199.65   $199.65   $199.60  
  Purchase #2 $164.52   12.485%   $185.0603   $185.06   $185.05   $185.10  
  Purchase #3 $159.60   8.458%   $173.099   $173.10   $173.10   $173.10  
  Purchase #4 $89.58   8.234%   $96.956   $96.96   $96.95   $97.00  
  Purchase #5 $5.64   12.326%   $6.3352   $6.34   $6.35   $6.30  
  Purchase #6 $95.79   9.526%   $104.915   $104.92   $104.90   $104.90  
  Purchase #7 $5.28   8.586%   $5.7333   $5.73   $5.75   $5.70  
  7 purchase totals = $699.26       $771.7455   $771.76   $771.75   $771.70