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 $108.49   8.124%   $117.3037   $117.30   $117.30   $117.30  
  Purchase #2 $118.43   11.145%   $131.629   $131.63   $131.65   $131.60  
  Purchase #3 $128.34   11.476%   $143.0683   $143.07   $143.05   $143.10  
  Purchase #4 $148.87   11.194%   $165.5345   $165.53   $165.55   $165.50  
  Purchase #5 $81.70   7.551%   $87.8692   $87.87   $87.85   $87.90  
  Purchase #6 $163.53   11.764%   $182.7677   $182.77   $182.75   $182.80  
  Purchase #7 $244.99   11.779%   $273.8474   $273.85   $273.85   $273.80  
  7 purchase totals = $994.35       $1,102.0198   $1,102.02   $1,102.00   $1,102.00