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 $192.61   13.719%   $219.0342   $219.03   $219.05   $219.00  
  Purchase #2 $84.28   4.126%   $87.7574   $87.76   $87.75   $87.80  
  Purchase #3 $174.40   7.522%   $187.5184   $187.52   $187.50   $187.50  
  Purchase #4 $96.30   9.798%   $105.7355   $105.74   $105.75   $105.70  
  Purchase #5 $110.55   11.521%   $123.2865   $123.29   $123.30   $123.30  
  Purchase #6 $185.84   8.131%   $200.9507   $200.95   $200.95   $201.00  
  Purchase #7 $216.83   5.413%   $228.567   $228.57   $228.55   $228.60  
  7 purchase totals = $1,060.81       $1,152.8497   $1,152.86   $1,152.85   $1,152.90