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 $203.62   11.320%   $226.6698   $226.67   $226.65   $226.70  
  Purchase #2 $92.77   9.745%   $101.8104   $101.81   $101.80   $101.80  
  Purchase #3 $49.64   4.613%   $51.9299   $51.93   $51.95   $51.90  
  Purchase #4 $84.78   5.621%   $89.5455   $89.55   $89.55   $89.50  
  Purchase #5 $91.85   5.620%   $97.012   $97.01   $97.00   $97.00  
  Purchase #6 $189.95   12.446%   $213.5912   $213.59   $213.60   $213.60  
  Purchase #7 $82.77   5.748%   $87.5276   $87.53   $87.55   $87.50  
  7 purchase totals = $795.38       $868.0864   $868.09   $868.10   $868.00