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 $109.50   11.693%   $122.3038   $122.30   $122.30   $122.30  
  Purchase #2 $212.79   13.116%   $240.6995   $240.70   $240.70   $240.70  
  Purchase #3 $15.89   4.666%   $16.6314   $16.63   $16.65   $16.60  
  Purchase #4 $249.58   8.626%   $271.1088   $271.11   $271.10   $271.10  
  Purchase #5 $167.85   10.478%   $185.4373   $185.44   $185.45   $185.40  
  Purchase #6 $184.64   4.447%   $192.8509   $192.85   $192.85   $192.90  
  Purchase #7 $179.90   9.221%   $196.4886   $196.49   $196.50   $196.50  
  7 purchase totals = $1,120.15       $1,225.5203   $1,225.52   $1,225.55   $1,225.50