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 $183.45   12.411%   $206.218   $206.22   $206.20   $206.20  
  Purchase #2 $108.46   10.778%   $120.1498   $120.15   $120.15   $120.10  
  Purchase #3 $155.97   13.835%   $177.5484   $177.55   $177.55   $177.50  
  Purchase #4 $220.44   6.350%   $234.4379   $234.44   $234.45   $234.40  
  Purchase #5 $87.46   11.642%   $97.6421   $97.64   $97.65   $97.60  
  Purchase #6 $126.29   4.436%   $131.8922   $131.89   $131.90   $131.90  
  Purchase #7 $243.94   5.762%   $257.9958   $258.00   $258.00   $258.00  
  7 purchase totals = $1,126.01       $1,225.8842   $1,225.89   $1,225.90   $1,225.70