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 $179.25   9.140%   $195.6335   $195.63   $195.65   $195.60  
  Purchase #2 $39.75   12.332%   $44.652   $44.65   $44.65   $44.70  
  Purchase #3 $109.79   12.284%   $123.2766   $123.28   $123.30   $123.30  
  Purchase #4 $66.44   9.675%   $72.8681   $72.87   $72.85   $72.90  
  Purchase #5 $108.33   11.387%   $120.6655   $120.67   $120.65   $120.70  
  Purchase #6 $163.70   3.463%   $169.3689   $169.37   $169.35   $169.40  
  Purchase #7 $187.92   8.666%   $204.2051   $204.21   $204.20   $204.20  
  7 purchase totals = $855.18       $930.6697   $930.68   $930.65   $930.80