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 $181.41   5.469%   $191.3313   $191.33   $191.35   $191.30  
  Purchase #2 $97.83   6.363%   $104.0549   $104.05   $104.05   $104.10  
  Purchase #3 $107.76   7.201%   $115.5198   $115.52   $115.50   $115.50  
  Purchase #4 $177.88   8.815%   $193.5601   $193.56   $193.55   $193.60  
  Purchase #5 $15.89   6.133%   $16.8645   $16.86   $16.85   $16.90  
  Purchase #6 $127.41   6.566%   $135.7757   $135.78   $135.80   $135.80  
  Purchase #7 $65.30   3.773%   $67.7638   $67.76   $67.75   $67.80  
  7 purchase totals = $773.48       $824.8701   $824.86   $824.85   $825.00