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 $196.96   3.832%   $204.5075   $204.51   $204.50   $204.50  
  Purchase #2 $172.92   8.304%   $187.2793   $187.28   $187.30   $187.30  
  Purchase #3 $76.52   8.606%   $83.1053   $83.11   $83.10   $83.10  
  Purchase #4 $38.29   12.763%   $43.177   $43.18   $43.20   $43.20  
  Purchase #5 $156.70   13.182%   $177.3562   $177.36   $177.35   $177.40  
  Purchase #6 $71.84   5.171%   $75.5548   $75.55   $75.55   $75.60  
  Purchase #7 $193.64   5.770%   $204.813   $204.81   $204.80   $204.80  
  7 purchase totals = $906.87       $975.7931   $975.80   $975.80   $975.90