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 $41.43   11.563%   $46.2206   $46.22   $46.20   $46.20  
  Purchase #2 $116.75   5.214%   $122.8373   $122.84   $122.85   $122.80  
  Purchase #3 $126.73   12.391%   $142.4331   $142.43   $142.45   $142.40  
  Purchase #4 $68.93   7.728%   $74.2569   $74.26   $74.25   $74.30  
  Purchase #5 $209.37   7.246%   $224.541   $224.54   $224.55   $224.50  
  Purchase #6 $213.73   9.776%   $234.6242   $234.62   $234.60   $234.60  
  Purchase #7 $160.60   7.554%   $172.7317   $172.73   $172.75   $172.70  
  7 purchase totals = $937.54       $1,017.6448   $1,017.64   $1,017.65   $1,017.50